Different mice have different allelic variants of class I MHC genes. Therefore, cytotoxic T cell (TC cell) clones can be generated by culturing lymphocytes harboring MHC allele A in the presence of nondividing nucleated cells harboring MHC allele B (and vice versa). These T cells can normally kill cells harboring allele B by inducing them to undergo apoptosis. Imagine two strains of mice with MHC allele A that are either wild type (WT) for the gene encoding perforin (A1) or are mutant and lack the gene (A2). Also imagine two strains of mice with MHC allele B that are either WT for the gene encoding Fas (B1) or are mutant and lack the gene (B2). Cytotoxic T cells derived from the A1 strain can induce apoptosis in both B1 and B2 cells. However, those derived from the A2 strain are only able to induce apoptosis in B1 cells and not B2 cells. Indicate whether each of the following statements is (Y) or is not (N) consistent with these observations. Your answer would be a four-letter string composed of letters Y and N only, e.g. NYNY.
( ) The perforin-granzyme pathway is the only way through which TC cells induce apoptosis in mouse target cells.
( ) The activation of the Fas-FasL pathway is sufficient to induce apoptosis by TC cells.
( ) There are other major pathways (not dependent on perforin or Fas) through which TC cells induce apoptosis in mouse target cells.
( ) Both pathways (Fas-FasL and perforin-granzyme) are required simultaneously for the induction of apoptosis by TC cells in mouse target cells.

Question

Different mice have different allelic variants of class I MHC genes. Therefore, cytotoxic T cell (TC cell) clones can be generated by culturing lymphocytes harboring MHC allele A in the presence of nondividing nucleated cells harboring MHC allele B (and vice versa). These T cells can normally kill cells harboring allele B by inducing them to undergo apoptosis. Imagine two strains of mice with MHC allele A that are either wild type (WT) for the gene encoding perforin (A1) or are mutant and lack the gene (A2). Also imagine two strains of mice with MHC allele B that are either WT for the gene encoding Fas (B1) or are mutant and lack the gene (B2). Cytotoxic T cells derived from the A1 strain can induce apoptosis in both B1 and B2 cells. However, those derived from the A2 strain are only able to induce apoptosis in B1 cells and not B2 cells. Indicate whether each of the following statements is (Y) or is not (N) consistent with these observations. Your answer would be a four-letter string composed of letters Y and N only, e.g. NYNY.
( )	The perforin-granzyme pathway is the only way through which TC cells induce apoptosis in mouse target cells.
( )	The activation of the Fas-FasL pathway is sufficient to induce apoptosis by TC cells.
( )	There are other major pathways (not dependent on perforin or Fas) through which TC cells induce apoptosis in mouse target cells.
( )	Both pathways (Fas-FasL and perforin-granzyme) are required simultaneously for the induction of apoptosis by TC cells in mouse target cells.

Quizplus · Accepted Answer

The ability of the A1 cytotoxic T cells to kill both B1 and B2 cells suggests that Fas in the target cell is not required to induce apoptosis; the perforin-granzyme pathway is sufficient. The ability of A2 cytotoxic T cells to kill B1 cells suggests that perforin in the TC cell is not essential either; activation of Fas is sufficient. Finally, the inability of A2 cytotoxic T cells to kill B2 cells suggests that at least one of these pathways (Fas-FasL or perforin-granzyme) should be functional for apoptosis to be induced and that there are no other major killing pathways in this cell system.

Different Mice Have Different Allelic Variants of Class I MHC