Which of the following is expressed by tumor cells to suppress T cells?
Rationale:
PDL1 is expressed by tumor cells to suppress T cells.
Tumor cells frequently upregulate Programmed Death-Ligand 1 (PDL1) on their surface. This
Which of the following isotypes of antibodies activate the complement cascade if bound to antigen?
Rationale:
IgM and IgG activate the complement cascade if bound to antigen.
IgM, typically a pentamer, is highly efficient at initiating the classical complement pathway by binding C1q after antigen recognition. IgG, specifically subclasses IgG1, IgG2, and IgG3, also effectively triggers complement activation upon antigen binding, although it requires multiple IgG molecules in close proximity for robust C1q engagement. These two antibody classes are primary mediators of complement-dependent cytotoxicity and opsonization.
A: IgA and IgD IgA primarily functions in mucosal immunity and does not activate the classical complement pathway; IgD's role is mainly as a B cell receptor, with no known complement activation function.
B: IgA and IgE IgA avoids classical complement activation; IgE is crucial for allergic reactions and parasitic defense, primarily through mast cell degranulation, not by initiating the complement cascade.
C: IgA and IgM While IgM is a potent complement activator, IgA actively avoids activating the classical pathway, thus making this combination partially incorrect regarding complement initiation.
Matching: Complement deficiency - Nonpitting edema
Rationale:
Complement deficiency of C1 inhibitor leads to nonpitting edema.
C1 inhibitor deficiency causes hereditary angioedema (HAE), characterized by recurrent episodes of nonpitting edema. The inhibitor normally regulates C1 activation and the kallikrein-kinin system. Its absence leads to uncontrolled bradykinin production, which dramatically increases vascular permeability, resulting in fluid leakage into interstitial spaces. This mechanism directly accounts for the observed swelling without pitting.
A: C5, 6, 7, 8, 9 These terminal complement components form the membrane attack complex. Deficiencies in these primarily predispose individuals to recurrent, severe infections by Neisseria bacteria, not typically causing nonpitting edema.
B: C3 C3 is central to all complement pathways. Its deficiency severely impairs opsonization and immune complex clearance, resulting in increased susceptibility to pyogenic bacterial infections and immune complex-mediated diseases, not nonpitting edema.
C: C1q C
In addition to recurrent staphylococcal abscesses and elevated serum IgE, the clinical manifestations of hyperimmunoglobulinemia E (hyper-IgE) syndrome frequently include which of the following?
Rationale:
Hyperimmunoglobulinemia E (hyper-IgE) syndrome frequently includes pneumatoceles as a clinical manifestation.
Pneumatoceles are a highly characteristic pulmonary manifestation of hyper-Ig
An 8-year-old child having coarse facial features seen by dentist because of failure to shed primary teeth and visited an orthopedician due to frequent fractures of lower limbs, now presented with skin abscesses and eczema. Of the following, the MOST likely diagnosis is
Rationale:
Hyper-IgE syndrome is the MOST likely diagnosis given the child's symptoms.
Correct Option Explanation:
Hyper-IgE syndrome, also known as Job's syndrome, perfectly matches the presenting symptoms. The coarse facial features, dental abnormalities like retained primary teeth, recurrent fractures, and chronic skin infections (abscesses, eczema) are classic manifestations of this primary immunodeficiency. This autosomal dominant disorder, often caused by STAT3 mutations, leads to impaired immune responses and connective tissue defects, explaining the diverse clinical picture.
Incorrect Options Explanation:
A: Nijmegen breakage syndrome This syndrome involves microcephaly, immunodeficiency, and increased cancer risk, but it doesn't typically present with coarse facial features, dental retention, or frequent fractures as prominent features.
B: Omenn syndrome Omenn syndrome is a severe combined immunodeficiency characterized by erythroderma, lymphadenopathy, and chronic diarrhea, presenting differently from this child's specific constellation of coarse features, dental issues, and fractures.
C: common variable immunodeficiency CVID primarily causes recurrent bacterial infections, particularly respiratory and gastrointestinal, and autoimmune manifestations. It lacks the characteristic skeletal, dental, and facial dysmorphic features seen in this patient.
You inject a mouse with an antigen that it has never been exposed to it before, the injection takes place at week 0 , at week 4 you inject the same mouse with the same foreign antigen, choose the right statement
Rationale:
IgM starts to appear after 2-3 days of week 0.
In a primary immune response to a novel antigen, B cells differentiate into plasma cells, initiating antibody production. IgM, as the first antibody class, typically becomes detectable in the bloodstream within 3 to 7 days following initial antigen exposure. This rapid, early synthesis provides crucial initial defense against the pathogen, preceding other antibody types.
B: IgM starts to appear after 2-3 weeks after week 4 This timeframe is significantly delayed for a secondary response, which is much faster and more robust, typically showing IgM within days, not weeks, after re-exposure at week 4.
C: IgM starts to appear after 2 weeks of week 0 Two weeks is an unusually protracted period for IgM's initial appearance following primary antigen stimulation, as its synthesis characteristically begins much earlier, often within the first week.
D: IgG appears
which of the following is wrong regarding Antimicrobial Peptides
Rationale:
Antimicrobial Peptides are Anionic peptides.
Antimicrobial Peptides (AMPs) are predominantly cationic, bearing a net positive charge. This crucial characteristic enables their electrostatic attraction to the negatively
A 45-year-old female presents with anorexia and some abdominal pain. Fecal smears reveal the presence of Taenia eggs, products of a parasitic tapeworm infection. Which one of the following cells would be most effective in defense against this parasite?
Rationale:
Eosinophils would be most effective in defense against this parasite.
Eosinophils are specialized granulocytes crucial for combating parasitic infections, particularly helminths like tapeworms. They release highly cytotoxic granules containing major basic protein and eosinophil cationic protein. These proteins effectively damage the parasite's tegument, mediating its destruction and removal from the host. Their specific cytotoxic mechanisms make them the primary cellular defense against Taenia eggs.
A: Platelets: Platelets primarily facilitate blood clotting and wound repair, contributing minimally to direct antiparasitic immunity. Their main function involves forming plugs and releasing factors for hemostasis.
B: Erythrocytes: Erythrocytes specialize in oxygen transport throughout the body via hemoglobin. They possess no direct phagocytic or cytotoxic mechanisms to combat parasitic invaders like tapeworms.
C:
A T cell located at the epithelial barrier of the gut is a
Rationale:
A T cell located at the epithelial barrier of the gut is a (γδ) T cell.
(γδ) T cells are uniquely abundant in epithelial tissues, particularly within the gut mucosa. These unconventional T cells recognize a broad range of stress-induced molecules and microbial antigens directly, without MHC presentation, playing a crucial role in immediate defense and tissue repair within the gut epithelial barrier. Their strategic location and innate-like functions make them primary responders there.
B: Helper T cell Helper T cells primarily orchestrate adaptive immune responses by secreting cytokines, typically residing in lymphoid organs or circulating. They require MHC class II presentation, a process not characteristic of direct epithelial barrier surveillance.
C: Cytotoxic T cell Cytotoxic T cells mainly eliminate virus-infected or cancerous cells by recognizing antigens presented on MHC class I. While present in tissues, they are not the predominant T cell population at the epithelial barrier itself for initial defense.
D: Regulatory T cell Regulatory T cells suppress immune responses to maintain tolerance and prevent autoimmunity, often found in lymphoid tissues and effector sites. Their primary role is immune modulation, not direct pathogen sensing at the immediate gut epithelial interface.
Antibodies in our body are produced by:
Rationale:
B-lymphocytes are responsible for producing antibodies in our body.
B-lymphocytes, specifically plasma cells derived from activated B cells, are the primary immune cells dedicated to synthesizing and secreting antibodies. Upon encountering specific antigens, B-lymphocytes undergo differentiation and proliferation, transforming into antibody-producing factories. These antibodies then circulate throughout the body, targeting and neutralizing pathogens, marking them for destruction by other immune components, forming a crucial part of humoral immunity.
B: T-lymphocytes T-lymphocytes primarily mediate cell-mediated immunity, directly killing infected cells or regulating other immune cells. They do not produce antibodies themselves but assist B cells.
C: Monocytes Monocytes are phagocytic white blood cells that differentiate into macrophages and dendritic cells, engulfing pathogens and presenting antigens. They lack the cellular machinery for antibody synthesis.
D: RBC's RBC's (red blood cells) are responsible for oxygen transport throughout the body. They are anucleated and have no immune function, therefore incapable of producing antibodies.
A 3-year-old girl presented with recurrent attacks of chest infection and frequent episodes of chronic diarrhea, stool examination revealed Giardia lamblia and serum IgA level was very low. Regarding this condition, all the following are true EXCEPT
Rationale:
Autosomal dominant inheritance is the exception.
Selective IgA deficiency, characterized by recurrent infections and low IgA, typically exhibits a multifactorial inheritance pattern, often involving multiple genes, or
A 9-year-old boy with acute lymphoblastic leukemia on chemotherapy, presented with fever, aphthous stomatitis, and fatigue for the last 5 days. His absolute neutrophil count (ANC) was 450/μL and hemoglobin level was 10 gm/dl. The NEXT appropriate therapeutic measure is
Rationale:
aggressive use of broad-spectrum antibiotics.
The patient exhibits febrile neutropenia (fever with ANC <500/µL), a life-threatening complication in immunocompromised
Which of the following immune system components would NOT recognize a macromolecule epitope (binding site)?
Rationale:
A phagocyte would NOT recognize a macromolecule epitope (binding site).
Phagocytes, such as macrophages and neutrophils, primarily internalize and digest foreign particles or cellular debris. While they possess pattern recognition receptors (PRRs) that identify general microbial patterns (PAMPs), these receptors do not typically recognize specific, pre-formed macromolecule epitopes in the same precise, antigen-specific manner as lymphocytes or antibodies do. Their role is broad engulfment, not specific epitope binding.
B: T lymphocyte T lymphocytes utilize T-cell receptors to specifically recognize processed peptide epitopes presented on MHC molecules by antigen-presenting cells, making them highly specific for macromolecular fragments.
C: B lymphocyte B lymphocytes directly bind specific, intact macromolecule epitopes via their surface B-cell receptors (membrane-bound antibodies), enabling highly precise antigen recognition without prior processing.
D: Antibody Antibodies are secreted proteins produced by plasma cells that precisely bind to specific macromolecule epitopes on antigens, facilitating their neutralization, opsonization, or agglutination.
Tissue mast cells
Rationale:
Tissue mast cells primarily function through the release of histamine and other mediators.
Mast cells are crucial immune cells located in connective tissues, particularly near blood vessels and nerves. Upon activation, typically by allergens binding to IgE antibodies on their surface, they degranulate, releasing preformed mediators like histamine, serotonin, and proteases. They also synthesize new mediators, including prostaglandins and leukotrienes. These substances orchestrate inflammatory responses, contributing to allergic reactions, wound healing, and defense against pathogens.
A: Phagocytosis and bacteriocidal mechanisms, antigen presentation Macrophages and dendritic cells primarily perform these functions, actively
Which of the following has an immunoglobulin fold?
Rationale:
BCRs & TCRs have an immunoglobulin fold.
Both B-cell receptors (BCRs) and T-cell receptors (TCRs) are members of the immunoglobulin superfamily. Their extracellular domains are characterized by distinctive immunoglobulin folds, which are beta-sandwich structures. These folds are crucial for antigen recognition and ligand binding, providing the structural framework necessary for adaptive immune responses. The shared structural motif underscores their evolutionary relationship and functional importance in immunity.
A: BCRs While BCRs possess immunoglobulin folds, this option is incomplete as TCRs also exhibit the same structural
Allows for flexibility
Rationale:
The hinge region allows for flexibility.
The hinge region, found between the Fab and Fc domains of an antibody, is a flexible polypeptide segment. Its unique amino acid composition, often rich in proline and cysteine, permits significant conformational changes. This structural adaptability is crucial, enabling the antibody's two antigen-binding sites to move independently, facilitating simultaneous binding to widely spaced epitopes on an antigen, thus enhancing immune complex formation.
A: Light chain The light chain contributes to the antigen-binding site but lacks inherent structural flexibility for the entire antibody molecule. It forms part of the Fab region, crucial for specificity, not global molecular movement.
B: Heavy chain The heavy chain provides the primary structural framework and forms both Fab and Fc regions. While essential for overall antibody function and defining isotype, it doesn't specifically confer the molecular flexibility observed in the hinge.
C: Fab region The Fab region is the fragment antigen-binding portion, responsible for recognizing and binding specific antigens. While its interaction with antigen is dynamic, the region itself is relatively rigid; the flexibility originates elsewhere.
Which of the following is used to enumerate and/or separate live cells that express an antigen, sorted by applying an electric charge to the stained cells?
Rationale:
FACS (fluorescence-activated cell sorting) is used to enumerate and/or separate live cells that express an antigen, sorted by applying an electric charge to the stained cells.
FACS precisely sorts and quantifies individual live cells based on their fluorescent properties. Cells are first stained with fluorochrome-conjugated antibodies targeting specific antigens. The instrument then hydrodynamically focuses the cells into a single stream, passes them through a laser, and detects their fluorescence. Droplets containing cells are charged according to their fluorescence, allowing electromagnetic deflection into distinct collection tubes, effectively separating them.
A: ELISA (Enzyme-linked immunosorbent assay) ELISA quantifies soluble antigens or antibodies in a sample using enzyme-linked detection, typically performed in microplates and not involving live cell sorting or electric charge application.
B: Fluorescent antibody (fluorochromes) Fluorescent antibodies are reagents used to label specific cellular components or antigens for visualization, but they are not a method for cell enumeration or electric charge-based sorting themselves.
D: Western blotting (immunoblotting)
Production of secreted antibodies (pAs site) involves a chain of amino acids with a stretch of charged (versus non charged) amino acids at the terminus, in comparison to membrane bound antibody production (pAm site).
Rationale:
Production of secreted antibodies (pAs site) involves a Shorter chain of amino acids with a stretch of charged amino acids at the COOH terminus.
Secreted antibodies are typically generated by alternative
Which of the following molecules is necessary (not accessory) for antigen recognition and T cell activation?
Rationale:
CD3 is necessary for antigen recognition and T cell activation.
CD3 is an indispensable component of the T cell receptor (TCR) complex, comprising invariant chains (gamma, delta, epsilon, zeta). It transduces the signal initiated by antigen binding to the TCR into the cell's interior, enabling T cell activation. Without CD3, the TCR cannot signal, making it absolutely essential for initiating downstream signaling pathways required for an effective immune response, thereby facilitating T cell activation.
A: CD2: CD2 is an adhesion molecule on T cells, binding CD58 on antigen-presenting cells to stabilize cell-cell interactions. While it contributes to T cell activation by providing co-stimulation, it is not fundamentally required for the initial antigen recognition signal transduction itself.
C: CD4: CD4 is a co-receptor on helper T cells, binding to MHC class II molecules. It enhances TCR signaling by bringing Lck into proximity with CD3, but the TCR-CD3 complex can still signal weakly without CD4, making it an accessory molecule.
D: CD8: CD8 is a co-receptor on cytotoxic T cells, binding to MHC class I molecules. Like CD4, it strengthens TCR signaling and recruits Lck, but it is not intrinsically part of the signal transduction complex itself, thus acting as an accessory molecule.
Ankylosing spondylitis
Rationale:
Ankylosing spondylitis is strongly associated with the HLA-B27 allele.
Ankylosing spondylitis, a chronic inflammatory disease primarily affecting the spine, exhibits a profound genetic predisposition linked to the HLA-B27 gene. Individuals carrying the B27 allele have a significantly elevated risk of developing the condition, demonstrating its critical role in disease pathogenesis. This major histocompatibility complex class I molecule is implicated in immune dysregulation, leading to the characteristic inflammation and fusion of vertebral joints seen in patients.
B: DR2 HLA-DR2 is associated with conditions like multiple sclerosis and narcolepsy, not ankylosing spondylitis. Its presence does not predispose individuals to the specific autoimmune pathology targeting spinal joints.
C: DR3 HLA-DR3 correlates with autoimmune diseases such as Sjögren's syndrome, Graves' disease, and type 1 diabetes. This allele does not show a significant genetic link to the development of ankylosing spondylitis.
D: DR4 HLA-DR4 is primarily linked to rheumatoid arthritis and specific forms of juvenile idiopathic arthritis. It does not confer susceptibility to ankylosing spondylitis, which has a distinct immunogenetic basis.
Mutations in TAP-1 or TAP-2 may alter the function of the heterodimer TAP. Which of the following is common for patients with TAP mutations?
Rationale:
Patients with TAP mutations commonly experience upper respiratory tract infections.
Mutations in TAP-1 or TAP-2 impair MHC class I antigen presentation, reducing the activation of cytotoxic T lymphocytes. This deficiency leaves individuals vulnerable to intracellular pathogens, particularly viruses, which are often cleared by CTLs. Consequently, these patients frequently suffer from recurrent viral infections, commonly presenting as upper respiratory tract infections due to compromised cellular immunity against these specific threats.
A: Human immuno-deficiency virus (HIV) infection HIV infection is a viral disease, but TAP mutations specifically affect endogenous antigen presentation, not primarily susceptibility to initial HIV acquisition itself, which involves different cellular entry mechanisms and immune evasion strategies.
B: Acquired immune deficiency syndrome (AIDS) AIDS is the final stage of HIV infection, characterized by severe immune depletion. While TAP mutations cause immune deficiency, it is distinct from the specific progressive T-cell destruction defining AIDS, which has a different etiology.
D: Coagulation disorders (hemophilia) Coagulation disorders like hemophilia involve defects in blood clotting factors or platelets. TAP mutations are immunodeficiency disorders affecting antigen presentation, having no direct causal link or mechanism related to blood clotting pathways.
Important role in allergic response; heparin & histamine
Rationale:
Basophils play an important role in allergic responses, releasing heparin and histamine.
Basophils are granulocytes that circulate in the blood and possess receptors for IgE antibodies, which are central to allergic reactions. Upon allergen exposure, cross-linking of IgE on their surface triggers degranulation, releasing potent inflammatory mediators like histamine, which causes vasodilation and increased permeability, and heparin, an anticoagulant, both crucial for acute hypersensitivity responses and inflammation modulation.
A: Natural Killer (NK) cells Natural Killer cells specialize in identifying and eliminating virus-infected cells and tumor cells without prior sensitization. Their primary function does not involve mediating allergic responses or releasing histamine and heparin.
B: Neutrophils Neutrophils are phagocytic cells vital for bacterial infection defense, engulfing pathogens and releasing antimicrobial compounds. They are not primarily involved in allergic reactions, nor do they release histamine or heparin.
D: T-cytotoxic cells T-cytotoxic cells (CD8+ T cells) recognize and destroy target cells presenting specific antigens, typically virus-infected or cancerous cells. Their immune function is distinct from immediate hypersensitivity reactions involving histamine and heparin.
Regarding mucosa-associated lymphoid tissue (MALT), which of the following is secreted by B cells across the epithelium?
Rationale:
IgA is secreted by B cells across the epithelium.
In mucosa-associated lymphoid tissue (MALT), plasma cells derived from activated B cells predominantly produce dimeric IgA. This specialized antibody is actively transported across epithelial cells into the lumen via the polymeric immunoglobulin receptor. Once secreted, IgA acts as a crucial first line of defense, neutralizing pathogens and toxins directly on mucosal surfaces without triggering inflammation, thus maintaining gut homeostasis.
B: IgD primarily functions as a B cell receptor on naive B lymphocytes, crucial for antigen recognition and activation. It is generally not secreted in significant amounts across epithelial barriers.
C: IgE is predominantly involved in allergic reactions and antiparasitic responses, binding to mast cells and basophils. It is not the primary immunoglobulin secreted across mucosal epithelia.
D: IgG is the most abundant antibody in serum, providing systemic immunity and crossing the placenta. While present in mucosa, it is not primarily secreted across epithelia by MALT B cells like IgA.
The activation of a naïve B cell, which generally requires a second accessory signal, occurs when the B cell exits the bloodstream and into a lymphoid organ, meets antigen, internalizes the BCR-antigen complex, and eventually becomes cells.
Rationale:
The activation of a naïve B cell, which generally requires a second accessory signal, occurs when the B cell exits the bloodstream and into a lymphoid organ, meets antigen, internalizes the BCR-antigen complex, and eventually becomes Primary; Plasma & memory cells.
Naïve B cell activation constitutes a primary immune
In contrast toαβ T cells, γδ T cells recognize certain peptide and nonpeptide antigens ___ processing and in the ___ of MHC class I and/or II molecules.
Rationale:
Without; Absence accurately describes how γδ T cells recognize antigens.
γδ T cells possess a distinct antigen recognition mechanism compared to conventional αβ T cells. They directly detect
Which of the following is a function of the adaptive immune system and NOT the innate immune system?
Rationale:
Distinguishes self from non-self is a function of the adaptive immune system and not the innate immune system.
The adaptive immune system possesses a sophisticated ability to differentiate between the body's own cells and foreign invaders, a crucial aspect of preventing autoimmunity. This self-recognition capability, developed through complex lymphocyte selection processes, ensures immune responses are precisely targeted against pathogens while tolerating healthy tissues. Innate immunity, conversely, primarily recognizes broad molecular patterns common to many microbes, lacking this fine-tuned self/non-self discrimination.
B: Has preformed or rapidly formed components
This characteristic describes the innate immune system, which relies on immediate, pre-existing defenses like phagocytes and complement proteins, or components quickly synthesized upon pathogen encounter, providing rapid initial protection.
C: Responds within minutes to infection
The innate immune system is characterized by its rapid, immediate response to pathogens, often within minutes or hours, utilizing pre-programmed mechanisms and cellular defenses to contain the initial spread of infection.
D: Has no specificity and responds to a range of pathogens
This describes the innate immune system's generalized approach, recognizing conserved pathogen-associated molecular patterns (PAMPs) common to many microbes, rather than specific antigens, thus offering broad but non-targeted defense.
A deficiency in complement inhibitors could lead to which of the following?
Rationale:
Hereditary angioedema could result from a deficiency in complement inhibitors.
Hereditary angioedema (HAE) is directly caused by a genetic deficiency in C1 ester
Activates TH2 and stimulates eosinophil production
Rationale:
Cytokines/TNF activates TH2 and stimulates eosinophil production.
Correct Option Explanation:
TNF-alpha, a potent pro-inflammatory cytokine, significantly activates TH2 responses by influencing antigen
Which of the following is NOT true regarding live viral vectored vaccines?
Rationale:
Live viral vectored vaccines do not require strong adjuvants.
Live viral vectored vaccines utilize replication-defective viruses to deliver antigens, effectively mimicking a natural infection. This inherent mechanism robustly stimulates both innate and adaptive immune responses, including strong T-cell activation, without needing additional immunostimulatory compounds. Their intrinsic immunogenicity means they are potent enough to elicit desired protection independently, making strong adjuvants largely superfluous for these highly effective vaccine platforms.
B: They are economical to produce
Viral vector production often leverages established cell culture systems, allowing for cost-efficient scalability once the initial development phase is complete, making them accessible for widespread use.
C: They can be delivered through needle-free methods
Some viral vectored vaccines are formulated for mucosal routes like intranasal or oral administration, circumventing the need for injections and potentially increasing vaccine uptake and ease of distribution.
D: They induce a broad and long-lasting immune response
By simulating natural infection, these vaccines effectively present antigens, stimulating comprehensive humoral and cellular immunity that typically confers durable and extensive protection against target pathogens.
A patient presents at age 6-months with pneumonia and difficulty fighting off infections of encapsulated bacteria and enteroviruses. A mutation in Bruton's tyrosine kinase (btk) is suspected. Which of the following is the most likely?
Rationale:
X-linked agammaglobulinemia is the most likely diagnosis.
A btk gene mutation causes X-linked agammaglobulinemia (XLA), impairing B-cell