Question 2 (5 points): The mouse thymus normally contains about 1-2 x 108 thymoc

Question

Question 2 (5 points): The mouse thymus normally contains about 1-2 x 108 thymocytes, the vast majority of which are CD4*CD8* (double-positive) cells. When thymocytes from mice with a gene deficiency in the TCRa locus are compared with those from TCRß-deficient mice, a striking difference between the two different knockout lines is observed, as shown in Figure A in a simplified version of flow cytometry data. The numbers of thymocytes in each thymus is indicated in the yellow bar below the plots Wild-type TCRa TCRp CD4 CD4 CD4 CD8 CD8 CD8 2 x 108 cells 2 x 108 cells 106 cells Figure A a). What do each of the populations seen in wild-type mice represent (in terms of DN, DP, CD4+ SP, and CD8+ SP thymoc/tes)? (2 points) b) What is the explanation for the difference in thymocyte subsets/populations and cell numbers observed when comparing TCRa to TCRB thymocytes? (2 points) c). Which region(s) of the thymus would show an absence of developing thymocytes in a thymus from a TCRa mouse? Which region(s) would have the absence in a thymus from a TCRß mouse? (1 point)

Explanation / Answer

a) In the wild type mice, the picture confirms that there is no possibility of DN( double negative) expression because in this category both CD 4 and CD 8 expression will be low. Here the picture also suggest that there is no DP (double positive) because in this case both CD 4 and CD 8 expression will be high. However here one expression is higher and others are at low hence it would be the possibility that CD4+ SP (Single positive) selection as it looks similar with other picture in TCR ?alpha deficincy .

b) The TCR alpha and beta thymocytes cell expression and differentiation depends upon the similar surface receptor and cell rearrangement since any one receptor is missing which can produce a significant effect on cell rearrangement which develops in the active at letter stage.

c) The TCR alpha cells to under alpha receptor differentiation and letter it has to be self recognized by MHC II peptide chain receptor for further development hence in case absence of MHC II receptor would lead to CD4 - negative selection (NP). In similar way the beta cells would undergo differentiation and self recognition by MHC I and in absence of MHC I would lead to CD8- negative selection (NP).

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