This parasite (Onchcerca volvulus) lives outside its host's cells (extracellular); therefore, cytotoxic T cells (CTLs) are ineffective in clearing the organism. This inability on the part of CTLs is due to their requirement to engage which of the following surface structures for their cytotoxic activity?
Rationale:
CTLs require engagement with the MHC class I-peptide complex for their cytotoxic activity.
Cytotoxic T lymphocytes (CTLs) specifically detect and eliminate host cells presenting intracellular pathogen-derived antigens via MHC class I molecules. Since Onchocerca volvulus resides extracellularly, it does not infect host cells or present its antigens through this pathway. Consequently, CTLs cannot identify target cells displaying parasitic peptides, making them ineffective against this extracellular organism. Their lytic function is strictly dependent on MHC class I presentation.
A: organism-specific antigen CTLs recognize pathogen-derived antigens, but only when presented on the surface of infected host cells within an MHC class I molecule. Direct engagement with free antigen alone does not activate their cytotoxic killing
Which of the following have not provided examples of secondary immunodeficiency?
Rationale:
High fat diet has not provided examples of secondary immunodeficiency.
Secondary immunodeficiency arises from external factors or underlying diseases that impair the immune system. While a high-fat diet can contribute to chronic
An article published in the Oncoimmunology journal in September 2018. It is discussing an immunotherapy approach that relies on designing and infecting the cancer patient two viruses expressing Melanoma-associated antigen A3 (MAGE-A3). The two viruses, a replication-deficient type-5 human adenoviral (Ad-MAGEA3) and Maraba MGI rhabdovirus(MGI-MAGEA3), are studied in this article preclinically by infecting nonhuman primates(monkeys). This immunotherapy approach is considered:
Rationale:
This immunotherapy approach is considered a Vaccination strategy.
The approach involves delivering tumor-associated antigen MAGE-A3 via two distinct viral vectors to nonhuman primates. This strategy aims to present the specific cancer antigen to the immune system, intending to provoke a targeted anti-tumor immune response, analogous to how traditional vaccines introduce pathogens to generate protective immunity against future infections. This antigen-specific delivery defines a vaccination approach.
B: Non-specific immune stimulation strategy This approach specifically delivers a defined tumor antigen (MAGE-A3) via viral vectors to elicit a targeted response, not broadly activating the immune system without antigen specificity.
C: Removing Immune-checkpoint blockade strategy The described method focuses on introducing a tumor antigen using viruses to stimulate immunity, rather than inhibiting immune checkpoints that suppress anti-tumor responses.
D: Small molecules strategy This immunotherapy utilizes complex biological entities—replication-deficient viruses—as delivery vehicles for an antigen, not synthetic low molecular weight compounds to modulate biological processes.
Matching: Immunodeficiency - Elevated IgE levels and eosinophilia
Rationale:
Hyper-IgE syndrome is characterized by elevated IgE levels and eosinophilia.
Hyper-IgE syndrome, also known as Job's syndrome, is a primary immunodeficiency disorder specifically defined by persistently high serum IgE levels, often exceeding 2000 IU/mL. This condition is also consistently associated with significant eosinophilia, recurrent skin abscesses, and other connective tissue and skeletal abnormalities. The combined presentation of elevated IgE and eosinophilia is a hallmark diagnostic feature of this particular syndrome.
A: Common variable immunodeficiency Common variable immunodeficiency presents with low levels of IgG, IgA, and often IgM, leading to recurrent bacterial infections. It does not typically feature elevated IgE or eosinophilia as defining characteristics.
B: Hyper IgM Hyper IgM syndrome involves normal or elevated IgM with very low or absent IgG, IgA, and IgE, due to defective class switching. Elevated IgE is contrary to its diagnostic criteria.
C: CD8 lymphocytopenia CD8 lymphocytopenia indicates a deficiency in cytotoxic T cells, increasing susceptibility to viral and opportunistic infections. This condition does not directly cause or is characterized by elevated IgE and eosinophilia.
Long-term treatment of the disease described in Question 27 is best accomplished with
Rationale:
Long-term treatment of the disease described in Question 27 is best accomplished with G-CSF.
G-CSF (Granulocyte-Colony Stimulating Factor) is crucial for long-term management of conditions involving chronic neutropenia, such as severe congenital neutropenia or chemotherapy-induced myelosuppression. It directly stimulates the proliferation and differentiation of granulocyte precursors in the bone marrow, thereby increasing circulating neutrophil counts. This elevation significantly reduces the frequency and severity of life-threatening infections, improving patient quality of life and survival outcomes effectively over extended periods.
A: prophylactic antibiotics These medications prevent infections but do not address the underlying bone marrow dysfunction causing chronic neutropenia, which is the primary issue requiring long-term treatment to restore immune function.
B: intravenous immunoglobulin IVIG provides passive immunity by supplying antibodies, useful for immune deficiencies or certain autoimmune conditions, but it does not stimulate the body's own neutrophil production or mitigate bone marrow failure.
C: interferon Interferons are immunomodulatory proteins used for viral infections or certain cancers and autoimmune diseases; however, they do not directly promote granulopoiesis or serve as a primary long-term therapy for neutropenic states.
C5, C6, C7, and C8 deficiency usually lead to
Rationale:
Recurrent meningococcal infections are typically caused by C5, C6, C7, and C8 deficiency.
Deficiencies in C5, C6, C7, or C8 components of the complement system impair the formation of the Membrane Attack Complex (MAC). The MAC is crucial for lysing Gram-negative bacteria, particularly Neisseria meningitidis. Without a functional MAC, individuals become highly susceptible to recurrent infections by this specific pathogen, leading to severe, life-threatening meningococcal disease. This specific vulnerability is a hallmark of these late complement component deficiencies.
B: encapsulated bacterial infections Encapsulated bacterial infections are more commonly associated with deficiencies in early complement components (C1-C4) or properdin, which impair opsonization and phagocytosis, not primarily the MAC-mediated lysis pathway.
C: glomerulonephritis Glomerulonephritis is often linked to immune complex deposition or specific complement dysregulation, such as C3 glomerulopathy, rather than isolated deficiencies of the late complement components (C5-C8) that primarily affect bacterial lysis.
D: atypical HUS Atypical Hemolytic Uremic Syndrome (aHUS) primarily results from dysregulation of the alternative complement pathway, often due to genetic mutations in complement regulatory proteins, not direct deficiencies in C5-C6-C7-C8 components.
the best sequence of inflammasome formation is
Rationale:
Inflammasome formation --- cleavage of caspas 1 --- cleavage of Pro IL-1 is the best sequence of inflammasome formation.
Inflammasome formation initiates the immune response by assembling specific protein complexes. This complex then recruits and activates pro-caspase-1, leading to its proteolytic cleavage into active caspase-1. Subsequently, active caspase-1 acts as a protease, cleaving inactive pro-interleukin-1β (Pro IL-1) into its mature, secreted form, driving inflammation. This sequential activation is crucial for proper immune signaling.
B: Inflammasome formation--- cleavage of Pro IL-1 --- cleavage of caspas 1 Pro-IL-1 cleavage cannot precede caspase-1 activation, as active caspase-1 is the essential enzyme responsible for processing pro-IL-1 into its mature, biologically active form.
C: Cleavage of Pro IL-1 --- inflammasome formation--- cleavage of caspas 1 Pro-IL-1 cleavage is a downstream event, requiring both inflammasome assembly and subsequent caspase-1 activation for its proteolytic processing into an inflammatory cytokine.
D: Inflammasome formation --- cleavage of caspas 8 --- cleavage of Pro IL-1 Caspase-8 is primarily involved in extrinsic apoptosis pathways and is not the protease directly activated by inflammasomes to cleave pro-IL-1; caspase-1 fulfills that specific role.
Wrong about MHC molecules
Rationale:
Cross presentation presents antigen on MHC II is wrong about MHC molecules.
Cross-presentation is a specialized pathway where exogenous antigens are processed and presented on MHC class I molecules, typically by dendritic cells, to activate CD8+ T cells. Conventional antigen presentation on MHC class II molecules involves endogenous processing of extracellular antigens to activate CD4+ T cells. Therefore, associating cross-presentation with MHC II is factually incorrect regarding immune mechanisms.
A: Variable between population MHC genes exhibit extreme polymorphism, leading to substantial allele variation among individuals and diverse genetic profiles across different human populations. This genetic heterogeneity is a defining characteristic of these crucial immune system components.
B: Variability causes different susceptibility to diseases between population The vast allelic diversity of MHC molecules directly influences antigen presentation capabilities, consequently determining varied immune recognition and differential population vulnerability to specific infectious agents or autoimmune conditions.
a person developed an extracellular bacterial infection With the subsequent release of IGM, what is the most What is the most important function of IGM in this infection
Rationale:
The most important function of IgM in this infection is complement receptor.
Correct Option Explanation:
Secreted IgM, particularly its pentameric form, is highly effective at activating the classical complement pathway. Upon
A person develops a viral infection and both T and B cells become activated to fight the infection. In which way is antigen recognition by B cells different from antigen recognition by T cells?
Rationale:
B cells utilize membrane immunoglobulin molecules to bind to antigen in its natural state.
B cells uniquely recognize antigens directly through their surface membrane-bound antibodies (immunoglobulins) in their native, unprocessed conformation. This direct binding to free antigens, or antigens on pathogens or surfaces, contrasts sharply with T cells, which require antigens to be processed into peptides and presented by Major Histocompatibility Complex (MHC) molecules on antigen-presenting cells for recognition.
A: B cells home to the paracortex of lymph nodes where they recognize the antigens trapped by helper T cells. B cells primarily reside in follicles, not the paracortex (a T cell zone), and recognize antigens directly, independent of T cell trapping.
B: B cells recognize the antigens that have been processed and presented by follicular dendritic cells. While follicular dendritic cells display unprocessed antigens, B cells themselves bind the antigen in its native form, not as a processed peptide.
C: B cells undergo receptor editing to change receptors that fail to bind to an antigen. Receptor editing primarily serves to modify self-reactive receptors during B cell development, not to alter receptors that merely lack affinity for foreign antigens.
which of the following is needed to ensure a healthy T cell army that doesn't attack our own cells?
Rationale:
TMECs are needed to ensure a healthy T cell army that doesn't attack our own cells.
Thymic Medullary Epithelial Cells (TMECs) are crucial for central tolerance. They express a wide array of self-antigens, enabling the selection process where developing T cells that strongly react to self-peptides are eliminated or rendered anergic. This vital negative selection mechanism, orchestrated by TMECs, prevents the maturation of autoreactive T cells, thereby safeguarding the body from autoimmune attacks by its own immune system.
A: MALTs Mucosa-Associated Lymphoid Tissues (MALTs) are peripheral immune sites involved in local immune responses, not the primary site for T cell education against self-reactivity.
C: APCs Antigen-Presenting Cells (APCs) present antigens to T cells, activating them in the periphery, but they do not primarily orchestrate the central tolerance mechanisms against self-attack.
D: all the above are needed Only TMECs directly perform the critical negative selection of T cells in the thymus, preventing autoimmunity, making this broad generalization inaccurate.
Eosinophilia can be seen in all the following EXCEPT
Rationale:
Eosinophilia is typically not seen in corticosteroid therapy.
Corticosteroid therapy is well-known to induce eosinopenia, meaning a decrease in eosinophil count, rather than eosinophilia. Corticosteroids suppress the production and release of eosinophils from the bone marrow and promote their sequestration in tissues, effectively lowering circulating levels. Therefore, eosinophilia would be an unexpected finding during corticosteroid administration, making it the exception among the given choices.
A: scabies Scabies infestations trigger a significant immune response involving IgE and T-helper 2 cells, consistently elevating eosinophil counts due to parasitic antigen exposure.
B: urticaria Urticaria, particularly chronic forms, often presents with elevated tissue and peripheral blood eosinophil levels, reflecting the allergic inflammatory pathways involved.
D: Hodgkin disease Hodgkin disease frequently presents with peripheral blood eosinophilia, a paraneoplastic phenomenon often linked to cytokine production by tumor cells.
To reduce the number of bacterial infection in patients with chronic granulomatous disease (CGD), they should be given daily
Rationale:
Patients with chronic granulomatous disease (CGD) should be given daily trimethoprim-sulfamethoxazole to reduce the number of bacterial infections.
Trimethoprim-sulfamethoxazole is a broad-spectrum antibiotic commonly used as prophylactic therapy in CGD patients. It effectively targets common bacterial and fungal pathogens that often cause severe, recurrent infections in individuals with impaired phagocyte oxidative burst function, which is characteristic of CGD. Daily administration significantly reduces the frequency and severity of life-threatening bacterial infections, improving patient outcomes and quality of life.
A: penicillin Penicillin primarily targets Gram-positive bacteria; its narrow spectrum does not adequately cover the diverse range
Which of the following components of the innate immune system involves cytokines produced by macrophages, which are produced during infection?
Rationale:
Interferons are cytokines produced by macrophages during infection as part of the innate immune system.
Interferons are a crucial class of cytokines, specifically produced by immune cells like macrophages and dendritic cells, particularly upon viral infection or other pathogen recognition. They play a vital role in initiating antiviral responses and modulating the immune system. Their production by macrophages directly links them to cytokine involvement during an infectious process, fitting the description precisely as an innate immune component.
A: Natural killer (NK) cells Natural killer cells are lymphocytes that directly kill infected or cancerous cells, operating independently of antibody or MHC presentation. While they produce cytokines, they are not themselves the cytokines produced by macrophages.
B: Complement system The complement system comprises a cascade of plasma proteins that enhance pathogen clearance through opsonization, lysis, and inflammation. It is a protein system, not a type of cytokine produced by macrophages.
C: Oxygen dependent and independent killing This refers to mechanisms used by phagocytes, like macrophages, to destroy internalized pathogens through reactive oxygen species or antimicrobial peptides. These are effector mechanisms, not the cytokines themselves produced by the macrophages.
Recognition of antigen
Rationale:
Cognitive phase is the recognition of antigen.
The cognitive phase precisely describes the initial encounter and specific binding of an antigen by immune cells. During this crucial stage, lymphocytes, particularly B and T cells, identify and attach to their corresponding antigenic determinants. This recognition event is fundamental, initiating the subsequent cascade of immune responses and ensuring specificity in targeting foreign pathogens or abnormal cells.
B: Activation phase The activation phase follows antigen recognition, involving cell proliferation and differentiation into effector and memory cells. It encompasses the expansion and maturation of lymphocytes, not the initial identification event itself.
C: Effector phase The effector phase involves the immune system actively eliminating the detected antigen. This stage includes mechanisms like antibody production, direct cell killing, and cytokine release, occurring after recognition and activation.
D: None of the above The immune response clearly involves distinct phases, and antigen recognition specifically falls within one of these initial stages, rendering this option inaccurate as a primary descriptor.
Which of the following differentiates an antigen from an immunogen?
Rationale:
An antigen does not always elicit an immune response.
An immunogen by definition is an antigen capable of triggering a specific immune response, leading to antibody production or T-cell activation. Conversely, an antigen is any substance that can specifically bind to components of the immune system, such as antibodies or T-cell receptors. Therefore, while all immunogens are antigens, not all antigens possess the necessary characteristics, like sufficient size or complexity, to initiate a full immune reaction.
A: An antigen is a foreign molecule. Both antigens and immunogens are typically foreign molecules, so this characteristic does not distinguish them. Self-antigens exist, but the key distinction lies in response generation.
B: An antigen can cause the production of antibodies. An immunogen specifically causes antibody production; an antigen merely binds to pre-existing antibodies or immune receptors, without necessarily initiating their synthesis.
D: Antigens are usually proteins or polysaccharides. Both antigens and immunogens are commonly proteins or polysaccharides due to their molecular complexity, making this a shared characteristic rather than a differentiator between them.
Can transfer across the placental (maternal protection)
Rationale:
IgG can transfer across the placental.
IgG is the only immunoglobulin capable of crossing the placental barrier from mother to fetus. This vital transfer provides passive immunity, protecting the newborn from various pathogens during the first few months of life before its own immune system fully develops. This maternal antibody transfer is a crucial mechanism for neonatal protection against common infections.
B: IgE IgE primarily mediates allergic reactions and parasitic infections; its molecular structure prevents efficient placental passage, thus offering no direct maternal protection to the fetus.
C: IgM IgM, a large pentameric antibody, is too large to traverse the placenta. It is typically produced by the fetus in response to in utero infections.
D: IgG & IgA While IgG crosses the placenta, IgA does not. IgA is predominantly found in secretions like breast milk, providing postnatal mucosal immunity to the infant.
Which of the following is only contained in heavy chains and not in light chains?
Rationale:
Diversity (D) is only contained in heavy chains and not in light chains.
The Diversity (D) gene segment is unique to immunoglobulin heavy chains, contributing significantly to their immense diversity. Light chains, both kappa and lambda, are assembled from V, J, and C segments, lacking this D segment. The combinatorial joining of V, D, and J segments in heavy chains, followed by VJ joining in light chains, creates the complete variable region, but only heavy chains incorporate the D segment for enhanced antigen recognition variability.
A: Leader (L) Leader (L) sequences are present in both heavy and light chains. They encode a signal peptide crucial for directing the nascent polypeptide into the endoplasmic reticulum, facilitating proper secretion and membrane insertion of the immunoglobulin molecule.
B: Joining (J) Joining (J) gene segments are found in both heavy and light chains. They connect the variable (V) segment to the constant (C) segment during V(D)J recombination, forming the complete variable region for antigen binding specificity in both chain types.
D: Variable (V) Variable (V) gene segments are fundamental components of both heavy and light chains. They form the primary antigen-binding site, undergoing somatic recombination with other segments to generate the diverse repertoire of antibodies capable of recognizing myriad antigenic determinants.
Which of the following TCR genetic chains contains V and J segments, similar to genes for immunoglobulin kappa and lambda light chains?
Rationale:
Gamma (γ); Alpha (α) TCR genetic chains contain V and J segments, similar to genes for immunoglobulin kappa and lambda light chains.
The alpha (α) and gamma (γ) chains of the T-cell receptor (TCR) both exhibit genetic organization involving Variable (V) and Joining (J) segments. This modular arrangement for antigen recognition is structurally analogous
MHC class I has three genes (HLA-A, HLA-B, & HLA-C). Which of the following is the correct order from most alleles (most polymorphic) to least alleles?
Rationale:
B > A > C is the correct order from most to least polymorphic for MHC class I genes.
HLA-B exhibits the highest degree of polymorphism among MHC class I genes, demonstrating the greatest number of alleles within the population. Following HLA-B, HLA-A possesses a substantial, though lesser, allelic diversity. HLA-C, while still polymorphic and crucial for immune function, displays the least allelic variation compared to the other two classical MHC class I loci, establishing the order B > A > C.
A: A > B > C This sequence incorrectly places HLA-A as the most polymorphic locus. HLA-B consistently demonstrates a significantly higher number of known alleles across human populations than HLA-A.
B: A > C > B This order misrepresents the relative polymorphism. HLA-A is not the most diverse, and HLA-B is far more polymorphic than HLA
Directly: carbohydrate, protein, lipid, nucleic acid epitopes
Rationale:
Immunoglobulin directly recognizes carbohydrate, protein, lipid, and nucleic acid epitopes.
Immunoglobulins, or antibodies, are secreted by B cells and serve as the primary effector molecules in humoral immunity. Their diverse antigen-binding sites, formed by variable regions of heavy and light chains, allow them to directly bind a vast array of molecular structures. This includes complex carbohydrates, proteins, lipids, and even nucleic acids found on pathogens or altered self-components, enabling broad recognition without requiring antigen presentation.
B: TCRαβ TCRαβ receptors on conventional T cells primarily recognize short peptide fragments derived from protein antigens, which must be presented within major histocompatibility complex (MHC) molecules, not direct, diverse epitopes.
C: TCR γδ TCR γδ receptors do display some direct antigen recognition for certain molecules; however, their range is more restricted than immunoglobulins and often involves specific stress ligands or unprocessed microbial products, not all biomolecules.
D: None of the above Immunoglobulins are definitively known for their extensive ability to directly recognize and bind a wide spectrum of diverse molecular structures, including carbohydrates, proteins, lipids, and nucleic acids, rendering this choice invalid.
B cell co-receptor phosphorylation sites include Igα/Igβ and which of the following?
Rationale:
B cell co-receptor phosphorylation sites include Igα/Igβ and CD19.
CD19 is a key component of the B cell co-receptor complex, alongside CD21 and CD81. Its cytoplasmic tail contains multiple tyrosine residues that become phosphorylated upon co-receptor activation, particularly by Src-family kinases. This phosphorylation creates docking sites for downstream signaling molecules like PI3K, crucial for amplifying B cell receptor signals and promoting B cell activation and survival.
B: CD20 CD
In the adult, the primary lymphoid organs, whose cells expand clonally, are the and secondary lymphoid organs, which create effector cells, are the , as well as mucosa associated lymphoid tissue (MALT) lining the respiratory, GI, and reproductive tracts.
Rationale:
In the adult, the primary lymphoid organs, whose cells expand clonally, are the Bone marrow and thymus and secondary lymphoid organs, which create effector cells, are the Spleen and lymph nodes, as well as mucosa associated lymphoid tissue (MALT) lining the respiratory, GI, and reproductive tracts.
Bone marrow and thymus are primary lymphoid organs where lymphocytes mature and develop immunocompetence, with B cells maturing in marrow and T cells in the thymus. Secondary lymphoid organs like the spleen and lymph nodes are sites where mature lymphocytes encounter antigens, proliferate, and differentiate into effector cells, orchestrating adaptive immune responses against pathogens.
A: Spleen and lymph nodes; Bone marrow and thymus This option incorrectly swaps the roles; spleen and lymph nodes function as secondary sites for immune activation, while bone marrow and thymus are crucial for lymphocyte development and maturation.
C: Spleen and bone marrow; Lymph nodes and thymus This choice mixes primary and secondary organs within both categories, failing to correctly distinguish between sites of lymphocyte maturation and those of antigen encounter and effector cell
During B cell development, when is there rearrangement in the heavy (H) chain of the immunoblobulin gene started?
Rationale:
Rearrangement in the heavy (H) chain of the immunoblobulin gene started during the Pro-B cell stage.
During the pro-B cell stage, hematopoietic stem cells have committed to the B cell lineage and initiate V(
At what stage does selection occur and where in the thymus does it occur?
Rationale:
Selection occurs at the DP stage in the cortex.
T-cell selection, encompassing both positive and negative selection, critically occurs during the Double Positive (DP) stage of thymocyte development. At this point, thymocytes express both CD4 and CD8 co-receptors. The anatomical location for these stringent selection processes is predominantly the thymic cortex, where DP thymocytes interact with cortical thymic epithelial cells to test their TCRs for appropriate MHC binding affinity, ensuring functional and self-tolerant T cells.
A: DN; Cortex The Double Negative (DN) stage represents an early developmental phase where thymocytes lack CD4 and CD8. TCR gene rearrangement occurs here, but the crucial positive and negative selection processes have not yet commenced.
C: SP; Cortex Single Positive (SP) thymocytes are cells that have already successfully undergone positive and negative selection, expressing either CD4 or CD8. These cells are exiting the cortex, not actively undergoing selection there.
D: DN; Subcapsular zone The Double Negative (DN) stage is too early for selection. While the subcapsular zone is an entry point for thymic progenitors, the rigorous positive and negative selection events do not occur there.
Which of the following is NOT true when comparing primary immune response to subsequent (secondary) immune response?
Rationale:
The statement "Secondary response has IgH (IgA or IgE) as the major antibody class" is NOT true when comparing primary immune response to subsequent (secondary) immune response.
Option D is incorrect because the major antibody class produced during a secondary immune response is primarily IgG, not IgH (which isn't a standard antibody class, likely a typo for IgA or IgE). While IgA and IgE play roles, IgG dominates secondary responses, providing long-lasting, high-affinity protection due to memory B cell activation and differentiation, ensuring rapid and robust pathogen clearance.
A: Primary response takes 5-10 days This statement is accurate; the initial immune reaction requires time for lymphocyte activation and clonal expansion before significant antibody production begins.
B: Secondary response takes 1-3 days This statement is accurate; memory cells facilitate a much quicker, more potent immune reaction upon re-exposure, rapidly producing antibodies and effector cells.
C: Primary response has IgM as the major antibody class This statement is accurate; IgM is the first antibody produced during initial antigen exposure, providing immediate, albeit lower affinity, pathogen neutralization and complement activation.
In the lectin complement pathway, mannan-binding lectin (MBL) indirectly activates which of the following components?
Rationale:
Mannan-binding lectin (MBL) indirectly activates C4 in the lectin complement pathway.
MBL, upon binding to pathogen surfaces, forms a complex with MBL-associated serine proteases (MASP-1 and MASP-2). MASP-2 is the key enzyme that cleaves C4 into C4a and C4b. C4b then binds to the pathogen surface, initiating the formation of the C3 convertase. Thus, MBL's action through MASP-2 leads to the activation of C4, making it an indirect activator.
A: C1: C1 belongs to the classical pathway, not the lectin pathway. Its activation involves antibody-antigen complexes or direct binding to pathogen surfaces, independent of MBL.
B: C2: C2 is cleaved by MASP-2 after C4 has been activated and deposited. MBL's direct enzymatic action is on
Which of the following is a chemoattractant that attracts neutrophils to the site of infection?
Rationale:
IL-12 is a chemoattractant that attracts neutrophils to the site of infection.
Correct Option Explanation:
IL-12, while primarily known for promoting Th1 differentiation and
Forms a pore in the target cell membrane (like MAC)
Rationale:
Perforin forms a pore in the target cell membrane (like MAC).
Perforin is a cytolytic protein crucial for immune surveillance, released by cytotoxic T lymphocytes and NK cells. It polymerizes within the target cell membrane, creating transmembrane channels or pores. These perforin pores facilitate the entry of other cytotoxic molecules, such as granzymes, into the target cell's cytoplasm, initiating apoptosis and ultimately leading to the demise of infected or cancerous cells, mimicking the membrane attack complex (MAC) function.
B: Granzyme Granzymes are serine proteases that enter target cells through perforin pores, then trigger apoptosis internally by activating caspases and other pathways, rather than directly forming membrane pores.
C: Fas ligand Fas ligand binds
An infant presents with recurrent bacterial infections and partial albinism. Lab work reveals giant granules and neutropenia. Which of the following is the most likely?
Rationale:
Chediak-Higashi disorder is the most likely diagnosis.
Chediak-Higashi disorder precisely manifests with recurrent bacterial infections due to impaired phagocyte function, causing neutropenia. The characteristic partial albinism results from defective melanin transport. Crucially, the presence of giant lysosomal granules within leukocytes, including neutrophils, is a pathognomonic finding for this rare autosomal recessive immunodeficiency, confirming the diagnosis described by the lab work.
A: DiGeorge's syndrome: This condition involves thymic aplasia, leading to T-cell deficiencies, hypocalcemia, and cardiac defects, which do not align with the described partial albinism or giant granules.
C: Chronic granulomatous disease (CGD): CGD involves defective phagocyte oxidative burst, causing recurrent infections with catalase-positive organisms, but it does not present with albinism, giant granules, or neutropenia.
D: Bare lymphocyte syndrome (BLS): BLS results from defective MHC class I or II expression, leading to severe combined immunodeficiency symptoms, which are distinct from the specific albin