immunology

What is the difference between innate and adaptive immunity?

Innate immunity is present from birth, non-specific, and doesn't require immunological memory. Adaptive immunity is acquired through antigen exposure, is highly specific, and generates memory.

Define antigen vs immunogen.

An antigen is any substance that interacts with antibodies or TCRs. An immunogen is an antigen capable of inducing a detectable immune response.

What is a hapten?

A small molecule that can react with antibodies but cannot induce an immune response on its own.

What is an epitope?

A single antigenic determinant - the specific part of an antigen that binds to an antibody or TCR.

Define affinity vs avidity.

Affinity is the strength of a single antigen-antibody binding interaction. Avidity is the overall binding strength when multiple binding sites are involved.

What is an adjuvant?

A substance that non-specifically enhances the immune response to an antigen.

Name the 5 immunoglobulin classes and their molecular weights.

IgG (150 kDa), IgA (160/400 kDa), IgM (900 kDa), IgD (180 kDa), IgE (190 kDa).

Which Ig is most abundant in blood?

IgG - the most prevalent immunoglobulin in circulation.

Which Ig is pentameric and largely restricted to the vascular pool?

IgM - comprises ~10% of normal blood antibody.

Which Ig predominates at mucosal surfaces?

IgA - found as dimers/polymers in secretions.

Which Ig is associated with allergy and atopy?

IgE - binds to mast cells and triggers Type I hypersensitivity.

Which Ig is important on B cell surfaces but has unclear function?

IgD - present on mature B lymphocytes.

What are the two types of light chains?

Kappa (κ) and Lambda (λ).

What do Fab and Fc fragments represent?

Fab = Fragment antigen-binding; Fc = Fragment crystallisable.

What is isotype (class) switching?

The process where B cells change their heavy chain production without changing antigen specificity.

What are complementarity determining regions (CDRs)?

Hypervariable loops in the V-region that form the actual antigen-binding site of antibodies and TCRs.

What surface marker identifies all T cells?

CD3.

CD4 is found on which cells?

Helper T cells, monocytes, macrophages, and dendritic cells.

CD8 is found on which cells?

Cytotoxic T lymphocytes (CTLs).

What is the difference between α/β and γ/δ T cells?

α/β T cells recognize peptide-MHC complexes; γ/δ T cells serve as first-line defense.

What are natural killer (NK) cells?

Cytotoxic lymphocytes that destroy target cells without prior sensitization.

What is a plasma cell?

A fully differentiated, antibody-secreting cell derived from B lymphocytes.

What are dendritic cells?

Professional antigen-presenting cells crucial for initiating adaptive immune responses.

What are Langerhans cells?

Dendritic cells resident in the epidermis.

What are Kupffer cells?

Liver-resident macrophages.

Name the three types of granulocytes.

Neutrophils, eosinophils, and basophils.

What is the primary function of neutrophils?

Phagocytosis of extracellular pathogens.

What is the primary function of eosinophils?

Anti-parasitic responses and roles in allergic reactions.

What is the primary function of basophils?

Release enzymes during allergic reactions.

Where is the MHC located in humans?

Short arm of chromosome 6.

What do Class I MHC molecules present and to which cells?

Present endogenous peptides to CD8+ cytotoxic T cells.

What do Class II MHC molecules present and to which cells?

Present exogenous peptides to CD4+ helper T cells.

What is encoded in the Class III MHC region?

Complement components and TNF.

What is MHC restriction?

T cells can only recognize antigen when presented by MHC molecules of the same haplotype.

What is β2-microglobulin?

A non-polymorphic protein that associates with Class I MHC molecules.

What are the two main complement pathways?

Classical pathway and Alternative pathway.

What is opsonisation?

Coating of pathogens with molecules that facilitate uptake by phagocytes.

What are anaphylatoxins?

Complement fragments (C3a, C5a) that increase vascular permeability and cause inflammation.

What is the terminal/lytic pathway?

The final complement cascade (C5-C9) forming the membrane attack complex (MAC) - common to both classical and alternative pathways.

What does CH50 measure?

The quantity/dilution of serum required to lyse 50% of RBCs in a haemolytic complement assay - tests overall complement function.

What is a cytokine?

A biologically active signalling molecule produced by cells that affects other cells by binding specific receptors.

What is the difference between autocrine and paracrine signalling?

Autocrine = cytokine acts on the same cell type that produced it. Paracrine = acts on nearby different cells.

What is the key function of IL-1?

Pro-inflammatory cytokine mediating inflammatory responses in innate and adaptive immunity.

What is IL-2's primary role?

T cell growth factor - promotes proliferation and differentiation of activated T cells, CTLs, and NK cells.

What does IL-4 do?

Stimulates T and B lymphocytes; key Th2 cytokine promoting antibody responses.

What does IL-5 do?

Stimulates B cell growth and eosinophil differentiation.

What is IL-6's role?

Stimulates B cell Ig production; major acute phase response cytokine.

What is IL-8 actually?

A chemokine (not a true interleukin) - chemoattractant for neutrophils.

What does IL-10 do?

Potent anti-inflammatory cytokine - limits host immune response to prevent tissue damage.

What do IFN-α and IFN-β do?

Type I interferons produced in response to viral infection - protect uninfected cells from viral spread.

What does IFN-γ do and who produces it?

Key Th1 cytokine; primary macrophage activator. Produced by NK cells, CD4+ Th1 cells, and CD8+ CTLs.

What is TNF's role?

Multifunctional pro-inflammatory cytokine involved in cell survival, proliferation, differentiation, and death.

What cytokine pattern defines Th1 vs Th2 cells?

Th1 = IFN-γ producers (cell-mediated immunity). Th2 = IL-4 producers (humoral/antibody immunity). Th0 = both.

What is hypersensitivity?

An exaggerated, inappropriate immune reaction against foreign compounds causing tissue damage.

What is anaphylaxis?

Immediate hypersensitivity (Type I) resulting from mast cell degranulation triggered by IgE-bound allergen.

What is atopy?

Genetic predisposition to hypersensitivity against common environmental antigens.

What is anergy?

A state of global immunological unresponsiveness.

What is tolerance?

A state where lymphocyte clones have been eliminated/inactivated by prior antigen contact, resulting in no immune response to that antigen.

What is autoimmunity?

Immune responses against self-antigens, often leading to autoimmune diseases (e.g., SLE).

What is clonal deletion?

Elimination of autoreactive lymphocyte clones in the thymus (T cells) or bone marrow (B cells) to establish self-tolerance.

What is molecular mimicry?

Cross-reactivity between pathogen antigens and self-antigens - proposed mechanism for some autoimmune diseases.

What is a graft-versus-host (GVH) reaction?

When immunocompetent donor cells attack tissues of an immunodeficient/histoincompatible recipient.

What is herd immunity?

When enough of a population is immune (via vaccination or infection) that disease transmission is blocked, protecting unimmunised individuals.

What are primary vs secondary lymphoid organs?

Primary = where lymphocytes develop (bone marrow, thymus). Secondary = where immune responses occur (lymph nodes, spleen, MALT).

What is GALT?

Gut-associated lymphoid tissue - includes Peyer's patches and mesenteric lymph nodes.

What are Peyer's patches?

Organised lymphoid tissue in the small intestine submucosa containing T cells and IgA-producing plasma cells.

What is secretory IgA (sIgA)?

Dimeric/polymeric IgA linked by J-chain, transported across epithelium with secretory component - predominant mucosal antibody.

What is the secretory component?

A ~95 kDa molecule produced by epithelial cells that binds to and protects IgA during transepithelial transport.

What are intraepithelial lymphocytes (IELs)?

T cell subset residing on basolateral surfaces of mucosal epithelia - can present antigen and act as natural killer T cells.

What is ELISA?

Enzyme-linked immunosorbent assay - uses enzyme-labelled antibodies/antigens to detect and quantify antigens/antibodies.

What is flow cytometry?

Technology analysing single cells passing lasers, measuring size (FSC), granularity (SSC), and fluorescence (from antibody staining or fluorescent proteins).

What is Western blotting?

Technique to identify specific proteins by gel separation, transfer to membrane, and detection with enzyme-labelled antibodies.

What is a hybridoma?

Immortal cell line created by fusing B cells with myeloma cells - produces monoclonal antibodies.

What is immunoprecipitation?

Formation of insoluble immune complexes to detect or isolate antigens.

What is the Ouchterlony technique?

Double immunodiffusion - antigen and antibody diffuse toward each other in agar gel forming precipitin lines.

What Baltimore group is HIV in and what does this mean?

Group VI - positive-sense single-stranded RNA virus with reverse transcriptase (ssRNA+ with RT step).

What Baltimore group are Measles and Influenza in?

Group V - negative-sense single-stranded RNA (ssRNA-). Influenza is segmented.

What Baltimore group are HCV and SARS-CoV-2 in?

Group IV - positive-sense single-stranded RNA (ssRNA+).

Which of the five viruses has the largest genome?

SARS-CoV-2 - approximately 29.9 kb (largest RNA virus genome).

Which virus has a segmented genome and why is this significant?

Influenza - segmentation allows reassortment between strains, enabling antigenic shift.

Which viruses replicate in the nucleus vs cytoplasm?

Nucleus: HIV, Influenza. Cytoplasm: Measles, HCV, SARS-CoV-2.

What is the R₀ for measles and why is it significant?

12-18 - the highest R₀ of common infections, meaning it's extremely contagious and requires ~95% vaccine coverage for herd immunity.

Rank the five viruses by R₀ (highest to lowest).

Measles (12-18) > HCV (3-4) > SARS-CoV-2 (2.9) > Influenza (2-3) > HIV (2-4).

What are the main transmission routes for HIV?

Sexual contact and blood-borne (sharing needles, transfusions).

What are the main transmission routes for HCV?

Blood-borne (contaminated needles, transfusions), very rarely sexual.

Which viruses are primarily airborne/respiratory?

Measles, Influenza, SARS-CoV-2.

What is HIV's primary receptor and co-receptors?

Primary: CD4. Co-receptors: CCR5 (R5-tropic) or CXCR4 (X4-tropic).

What receptors does Measles virus use?

CD46 and SLAM (signalling lymphocyte activation molecule).

What receptor does Influenza use?

Sialic acid residues on cell surface glycoproteins.

What receptors does HCV use?

CD81 (primary), plus GAG, LDL-R, HSPG, Claudin, and Occludin (co-receptors).

What receptor does SARS-CoV-2 use?

ACE2 (angiotensin-converting enzyme 2).

Is HIV cytopathic?

Yes and no - directly kills some CD4+ T cells but also causes indirect death through immune activation.

Is HCV cytopathic?

No - liver damage is primarily immune-mediated, not direct viral killing.

Is SARS-CoV-2 cytopathic?

No - pathology largely from immune response/inflammation.

What diseases can chronic HCV infection cause?

Hepatic inflammatory flares → fibrosis → cirrhosis → hepatocellular carcinoma (HCC). Also associated with Type 2 diabetes (extrahepatic manifestation).

What is Long COVID?

Persistent symptoms following SARS-CoV-2 infection, lasting weeks to months after acute illness.

What is antigenic drift vs antigenic shift?

Drift = gradual mutation accumulation (point mutations). Shift = major changes from genome segment exchange between strains (reassortment) - only occurs in segmented viruses like Influenza.

Which of the five viruses has NO approved antivirals?

Measles - relies entirely on vaccination for control.

Name the main classes of HIV antiretrovirals.

Entry inhibitors (EI), Fusion inhibitors (FI), Attachment inhibitors (ATTI), NRTIs, NNRTIs, Integrase inhibitors (II), Assembly inhibitors (ASSI), Protease inhibitors (PI).

What class is Maraviroc (MVC)?

Entry inhibitor - blocks CCR5 co-receptor.