B-cell activation - Answer a) Antigen binds to a receptor on the B-cell
b) Antigen is internalized by receptor-mediated endocytosis
c) B-cell displays antigen on its cell membrane as a peptide:MHC class II complex (B-cell
is acting as an APC)
d) CD4 TH2 cell recognizes and binds to the complex
e) The binding of the complex induces the expression of costimulatory molecules
CD40L and CD28 on the T cell and CD40 and B7 on the B-cell
f) CD40L-CD40 and CD28-B7 bind together
g) The T-cell secretes cytokines, which binds to their associated receptor on both
cells (both paracrine and autocrine)
h) B-cells are differentiated into plasmocytes and memory-B cells
T cell activation - Answer a) CD4 TH1 cells bind to an APC, forming an immune synapse
Arranged in a pattern with three rings of clusters of cells with similar functions,
called supra molecular activating clusters (SMAC)
- Signal molecules (cSMAC): central ring, contains the molecules responsible
for signalling between the TCR and peptide:MHC molecules
- Adhesion molecules (pSMAC): middle ring, contains adhesion proteins (eg. integrins and
cytoskeletal linker proteins) that keep the cells long enough for signals to propagate
,- Signal regulation molecules (dSMAC): outer ring, consists of proteins that help regulate
signal transduction
b) Activate CD8 cells, which initiates cell-mediated immunity
Interleukins - Answer - Regulate immune responses
- Affect proliferation and differentiation of hematopoietic/immune cells
Interferons - Answer - Most common types are alpha, beta, and gamma IFNs
- Induce an antiviral state to inhibit viral replication
- Regulate immune responses
Tumor necrosis factor - Answer - Most common types are alpha and beta TNFs
- Involved in systemic inflammation (septic shock) and tumour regression
- Can cause apoptosis
Cell-mediated immunity (T-cells) - Answer CD8 cytotoxic cells kill identified cells
that have been infected with viruses
Humoural immunity (B-cells) - Answer plasmocytes produce antibodies
Types of antibodies - Answer - surface antibodies: form part of the B-cell receptor on
the membrane)
- soluble antibodies: secreted by plasmocytes and circulate freely in the blood)
Functions of antibodies - Answer - Neutralize biological effect of pathogen
- Mark pathogen for phagocytosis (opsonization)
- Activate MACs to lyse the pathogen
Structure of antibodies - Answer - Heterodimeric proteins held together by disulfide
bonds
- Two light chains form the antigen-binding regions
- Two heavy chains form the Fc region (interacts with immune cell receptors)
Classes of antibodies - Answer IgM, IgG, IgA, IgE, IgD
IgM - Answer - Forms a pentamer
- First antibody to be formed in an immune response
- Activates the complement, which then amplifies the inflammatory and
adaptive immune response
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