25. Receptor (B and T) diversity results from a. somatic recombination of germli

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25. Receptor (B and T) diversity results from a. somatic recombination of germline configuration of genes in variable regions b. the imprecision of the "cut and paste" mechanism of somatic recombination c. different combinations of the chains making the receptors d. all of the above e. a and b only 26 How do antigenic peptides move from a cel's cytoplasm to its surface? a. attached to major histocompatability molecules which will become part of cell's surface b. in membrane bound vesicles c. they diffuse to the surface d. carried by ribosomes 27. The action of natural killer cells (NK) continues until a. antibody is produced b. infection is stopped c, the infection kills the patient d. cytotoxic T cells arrive e. b and d f a and d 28. Which is not true about the acute phase response? a. acute phase proteins act by neutralization not opsonization b. trigger the lectin and classical pathways of complement activation c. acute phase proteins are made in hepatocytes (liver cells) d. activated by cytokines 29. Functions of CD4 T(helper) cells include all of the following except a. help macrophages kill infected cells b. kill cells infected with viruses c. secrete cytokines which attract phagocytes d. stimulate B cells to become plasma cells 30. Protective antimicrobial peptides produced by various epithelial cells are: a. defensins b. adhesins c. integrins d. kinins 31. Which of the following is true about antibodies? a. produced by T cells b. kills infected cells by depositing toxic substances on its surface c. are exactly like B-cell receptors d. recognizes a part of macromolecules in the cell surface of the pathogen 32. Neutrophils a. leave circulation in response to macrophage signals b. live for months c. have adhesion molecules on surface which help with extravasation d. least common leukocyte e. a, b, andd f a and c

Explanation / Answer

Answers:

25. (d). All of the above.

Our immune system needs to recognize a large variety of foreign invaders. For this to happen, diversification of the B and T cell receptors on the lymphocytes is a requisite. For this a number of mechanisms are adopted some being;

26. (a) Antigenic peptides move from the cell cytoplasm to the cell surface are attached to newly formed major histocompatibility complex I molecule and targeted onto the cell membrane.

Mechanism: The process begins with degradation of self as well as pathogenic proteins(proteolysis), digested by proteasomes to form peptides which are transported to the Endoplasmic Reticulum. In the ER, they combine with MHC I molecules and reach the surface and becomes a part of it.

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