Lymphocyte Function

Question 1

What are all lymphocytes? How is this achieved?

What is the receptor for B cells?

T cells?

How many variants of B and T cells each with different specificity exist?

What is a clone?

Answer 1

• All lymphocytes are antigen specific, specificity is achieved by antigen receptor on cell surface.
• B cells: receptor = cell-surface antibody
• T cells: receptor = T cell receptor (TCR)
• 10¹¹
• Cells of same specificity are a clone

Question 2

Answer 2

Question 3

How do B cells produce immunoglobulin?

Answer 3

B cells must first be activated by binding to antigen, then b cells differentiate into plasma cells which actively produce Ig

Question 4

How is generation of antibody diversity achieved?

What are the segments for:

• Variable Heavy (VH) domains
• Variable Light (VL) domains
• Constant domains

Answer 4

• antibodies are encoded by multiple gene segments

VH: Variable, Diversity and Joining genes

VL: Variable and Joining genes

C: Constant genes

Question 5

What immunoglobulin do all B cells begin by making first?

What is class switching?

Answer 5

• IgM
• Class switching occurs in the secondary response, when memory cells produce IgG, IgA or IgE with same antigen specificity as the IgM originally developed in the primary response

Question 6

What is the T cell receptor?

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Answer 6

• structure on T cell surface that recognises antigen
• structurally related to immunoglobulin
• similar complex gene structure: V, D, J, C gene segments encoding V and C regions
• binds to antigenic peptide associated MHC

Question 7

What distinguishes a helper T cell from a cytotoxic T cell?

Answer 7

The cell surface proteins CD4 and CD8:

• Helper T cells are associated with CD4 and CD3
• Cytotoxic T cells are associated with CD8 and CD3

Question 8

T cell help with MHC Class II - list the steps:

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List some responses of CD4+ T cells:

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Answer 8

• after binding to antigen, T_h cells secrete growth factors (cytokines) which control the immune response
• these cytokines are produced in small amounts and act locally
• CD4+ T cells secrete cytokines which control and coordinate immune response
• some CD4+ T cells favour macrophage activation and cell-mediated responses
• others stimulate B cells to produce antibodies

Question 9

Cell mediated cytotoxicity

Answer 9

After binding antigen, activated T_c:

• release perforins which form pores in target cells
• repease other damaging enzymes
• release cytokines

TNF triggers apoptosis, helped by IFN