Items 45-51
The surfaces of B cells and T cells possess functionally important receptors (antigens) which determine their immunological roles. For each numberee description receptors (antigens) which determine their immunological roles. For each numbered description of structure or functions, choose the most appropriate lettered antigen. Answers may be used once, or not at all.
(A) T cell receptor
(B) CD3 antigens
(C) CD4 antigens
(D) CD8 antigens
(E) LFA -3
(F) ?2-microglobulin
(G) Class I MHC ( Major Histocompatibility Complex)
(H) Class II MHC
(I) Class III MHC
(J) CD2 antigen
(K) B7
(L) CD28 antigen
(M) CD40 antigen
45. Monomeric heavy chain, MW = 44,000B; membrane anchored; three cytoplasmic domains; present n virtually all cells; associated with smaller protein; present foreign antigen to cytotoxic T lymphocytes.
46. Polypeptide of MW = 12,000; associated non-convalently with both class I and II MHC.
47. Two distinct polypeptides ( a and ? ), having barable, diverse and constant segments; found complexed with CD3 proteins.
48. Two distinct polypeptides, MW = 34,000 and 29.000, both membrane anchored; two cytoplasmic domains each, present on B cells, activated T cells and macrophages; restricts helper functions.
49. An assemblage of at least for distinct membrane-bound polypeptides, some forming heterodimers, all found in conjunction with the T cell receptor.
50. Two distinct polypeptides, a and ?, MW = 40,000 and 50,000; present on helper and cytotoxic T cells; recognizes MHC embedded antigen.
51. Glycoprotein, MW = 50,000, found on mature T cells, natural killer cells and thymocytes; binds to the lymphocyte function antigen -3 ( LFA – 3).
ANSWERS AND TUTORIAL ON ITEMS 45-51
The answers are: 45-G; 46-F; 47-A; 48-H; 49-B; 50-A; 51-J. The antigens present on T cells vary in their molecular composition and function. Many possess multiple domains which determine how they will be situated within the cell membrane and interact with other T cell antigens.
The a ? T cell receptor ( A) recognizes the processed antigen fragment presented by the antigen presenting cells through their class II MHC. The T cell receptor interacts with cell surface antigens which functionally define cytotoxic, CD8 (D), or helper, CD4 (C), functions. Class II MHC (H) antigens , present on immunocompetent cells such as B cells, macrophages and activated T cells, functions to restrict helper functions. Class I MHC (G) antigens, present on all cells, restrict the targeted killing effects of cytotoxic cells. Both MHC classes form noncovalent associations with the B2-microglobulin (F) found on T cell surfaces. The CD3 antigens (B) comprise at least four different membrane bound polypeptides which associate with the T cell receptor in different orientation. The proteins, designated Y, ?, ? and ?, interact individually, as heterodimers and homodimers under different situations. For example, the CD3 complex is thought to be involved to be involved in transmembrane signaling. Cell activation via the CD3 complex results in elevation of intracellular Ca²+ and phosphorylation of CD3 subunits. The rearrangement of these antigens may be functionally altered in tumor cells rendering them unrecognizable by cytotoxic T cells. The MHC III antigens (I) consist of C2, C4 and B complement components. boom Mounted Microscopes Articulating microscope, Boom Mounted Microscopes Dual Arm type of microscope, Boom Mounted Microscopes with Mobile Floor Stand Boom Mounted Microscopes. Other cell-to cell interactions must also occur for T cell activation to occur. Interactions such as the binding of LFA-3 (E) (on the surface of T cells) to the Cd2 antigen (J) (on the antigen presenting cell) must occur. Blockage of LFA-3 with antibody prevent T cell signaling. The specific ligand for other T cell antigens, such as CD45, has not been identified. Recent results suggest that antigens found on tumor cells, e.g. the B7 antigen (K), present on the surface of certain mouse tumors, act as a costimulator of cytotoxic T cell with MHC I and T cell receptor comprising the primary recognition interaction, induces multiplication of T cells able to recognize the previously ignored target cells.
The CD40 antigen (M), present on B cells, interacts with its corresponding ligand which is present on activated T cells. This allows B cells to switch form expanding IgM to other immunoglobulins. Different cytokines determine which immunoglobulin will eventually be expressed by the activated B cells. Teaching Microscopes, Toolmakers Microscopes.
