Immunology Flashcards
What are Natural Killer (NK) cells?
NK cells are innate lymphocytes that play a crucial role in the immune response by recognizing and killing virus-infected cells and tumor cells without prior sensitization.
Which lineage do NK cells belong to?
NK cells belong to the lymphoid lineage, but they are part of the innate immune system.
What are the major surface markers of NK cells?
NK cells express CD16 and CD56 as their major markers.
Also CD94
What is the role of CD16 in NK cells?
CD16 (FcγRIII) mediates antibody-dependent cellular cytotoxicity (ADCC) by binding to the Fc portion of IgG.
What is the role of CD56 in NK cells?
CD56 is an adhesion molecule involved in NK cell activation and interaction with other immune cells.
Mechanism of NK cells
It has activating and inhibitory arm
Cells with MHC1 will get the inhibitory arm.
Cells with virus/ cancer won’t have MHC1 and it gets the activating arm which has NKG2D
Which cytokines activate NK cells?
IL-2, IL-12, IL-15, and IL-18 enhance NK cell activity.
What is the key difference between NK cells and cytotoxic T lymphocytes (CTLs)?
Unlike CTLs, NK cells do not require prior antigen exposure or MHC class I presentation to kill target cells.
What are the two main pathways by which NK cells induce apoptosis?
Perforin-granzyme pathway – Releases perforin to create pores and granzymes to induce apoptosis.
Fas-FasL pathway – NK cells express FasL, which binds to Fas on target cells, triggering apoptosis.
Which infections are more common in individuals with NK cell deficiency?
Individuals with NK cell deficiency are more susceptible to herpesviruses (e.g., CMV, HSV, EBV) due to impaired viral clearance.
Which clinical conditions are associated with defective NK cell function?
Severe herpesvirus infections (CMV, EBV, HSV)
Chronic lymphocytic leukemia (CLL)
Primary NK cell deficiency
What is the Pan T cell marker that carries the signal transduction molecule?
CD3
Helper T cell? Cytotoxic T cell?
CD4, CD8
Ratio of CD4 to CD8
CD4=2
CD8=1
If CD4:CD8 count is reducing, it is?
If CD4: CD8 count is increasing, it is?
HIV
Sarcoidosis
Where do T cells mature?
T cells mature in the thymus, where they undergo positive and negative selection.
What are the two main types of T cells?
CD4+ T helper cells (Th cells) – Help other immune cells by secreting cytokines.
CD8+ Cytotoxic T cells (CTLs) – Kill infected and cancerous cells.
What is the function of CD4+ T cells?
CD4+ T cells recognize MHC class II on antigen-presenting cells (APCs) and help coordinate the immune response through cytokine secretion.
What is the function of CD8+ T cells?
CD8+ T cells recognize MHC class I on infected or cancerous cells and kill them using perforin and granzyme-mediated apoptosis.
What is the role of regulatory T cells (Tregs)?
Tregs (CD4+CD25+FOXP3+) suppress excessive immune responses to maintain self-tolerance and prevent autoimmune diseases.
What are the key surface markers of T cells?
CD3 – TCR signaling complex (all T cells)
CD4 – Helper T cells (binds MHC II)
CD8 – Cytotoxic T cells (binds MHC I)
CD25 & FOXP3 – Regulatory T cells
CD28 – Co-stimulatory receptor for activation
Which infections are associated with CD8+ T cell dysfunction?
HIV/AIDS – Causes CD8+ T cell exhaustion
Chronic hepatitis B/C – Leads to persistent CD8+ T cell activation and dysfunction
Which genetic mutations cause T cell immunodeficiencies?
SCID (Severe Combined Immunodeficiency) – Defective T cell development
DiGeorge Syndrome – Thymic hypoplasia leading to T cell deficiency
FOXP3 mutations – IPEX syndrome (autoimmunity due to lack of Tregs)
What are the major subsets of CD4+ T helper cells?
Th1 cells – Secrete IFN-γ, activate macrophages, and are involved in intracellular pathogen clearance.
Th2 cells – Secrete IL-4, IL-5, and IL-13 to promote B cell antibody production and eosinophilic response.
Th17 cells – Secrete IL-17 and IL-22 to enhance neutrophil responses against extracellular bacteria and fungi.
What is the role of T cells in transplant rejection?
Acute rejection – CD8+ T cells attack donor tissue.
Chronic rejection – CD4+ T cells mediate chronic inflammation.
What is the role of T cells in autoimmune diseases?
Th1 dominance → Type 1 diabetes, MS
Th17 dominance → Psoriasis, IBD
Treg dysfunction → Autoimmune polyendocrine syndromes
What are the two main types of TCRs? (T cell Receptor)
αβ TCR – Found on most T cells, involved in adaptive immunity.
γδ TCR – Found in mucosal and epithelial tissues, involved in innate-like immunity.
T cell CD markers
CD1-8, 28
CD markers of B cell
CD10 (CALLA)
CD19, 20, 21, 22, 23
CD40
CD79a, 79b
Pan B cell marker
CD19
Signal transduction molecule for B cells
CD79
How does EBV enter the B cell
CD21
Interaction between B and T cells
B cells have CD40 and T cells have CD40 ligands. These interact and T cells produce IL-4
IL-4 changes IgM to IgG, A, M, E, D- This is called Isotype switching.
Defect in this causes Hyper IgM syndrome
What is the Major Histocompatibility Complex (MHC)?
MHC is a set of cell surface proteins that present antigens to T cells
What are the two main types of MHC molecules?
MHC Class I – Present on all nucleated cells; recognized by CD8+ T cells.
MHC Class II – Present on antigen-presenting cells (APCs); recognized by CD4+ T cells.
Where are MHC genes located?
On chromosome 6, within the Human Leukocyte Antigen (HLA) complex.
What are the genes encoding MHC Class II molecules?
HLA-DP, HLA-DQ, and HLA-DR.
What are the genes encoding MHC Class I molecules?
HLA-A, HLA-B, and HLA-C.
Which cells express MHC Class I?
All nucleated cells (except RBCs).
Which cells express MHC Class II?
Antigen-presenting cells (APCs):
Dendritic cells (most potent APCs)
Macrophages
B cells
What type of antigens does MHC Class I present?
Endogenous antigens (e.g., viral or tumor antigens).
What type of antigens does MHC Class II present?
Exogenous antigens (e.g., bacterial toxins).
HLA 3 makes ___
Complement proteins such as C2, C4, HSP, TNF alpha
Antigen binding clefts in MHCs
MHC1- Alpha1 Alpha2 junction
MHC2- Alpha1 Beta2 junction
What is the role of MHC in organ transplantation?
Mismatched MHC molecules can trigger graft rejection.
HLA matching is crucial for successful transplants.
What is superantigen activation of MHC?
Superantigens (e.g., Staphylococcal enterotoxins) bind MHC II and TCR without antigen specificity, causing a cytokine storm (e.g., toxic shock syndrome).
Which HLA types are associated with autoimmune diseases?
HLA-B27 → Ankylosing spondylitis
HLA-DR3/DR4 → Type 1 diabetes
HLA-DR4 → Rheumatoid arthritis
HLA-DR2 → Multiple sclerosis
What is TAP deficiency (Bare Lymphocyte Syndrome Type I)?
A defect in TAP transporter prevents MHC I antigen loading, leading to recurrent viral infections.
What is Bare Lymphocyte Syndrome Type II?
A defect in MHC II expression, leading to defective CD4+ T cell activation and severe immunodeficiency.
Types of Hypersensitivity reactions
ACID
Anaphylaxis
Cytotoxic
Immune complex
Delayed
