10 Jun The inbred mouse strains BALB/c and C57BL have different
Question
2. The inbred mouse strains BALB/c and C57BL have different Ig heavy chain allotypes: The BALB/c allele is IgHa, whereas the C57BL allele is IgHb. C57BL mice make good immune responses to the antigen “Z”, but BALB/c mice respond poorly. Assume you produced (BALB/c X C57Bl)F1 mice, then back-crossed these F1s to BALB/c. You tested 100 of the back-cross progeny for allotype(s) expressed in their serum, and for their ability to make anti-Z responses. The number of back-cross mice in each possible category are shown in Table 1:
Table 1. Immune response and IgH phenotypes of back-cross progeny
Anti-Z responsive? IgHa only IgHa and IgHb
yes 25 25
no 25 25
A second experiment was done to further examine this intriguing “responder-non-responder” phenomenon. In this experiment, T and B cells from the two strains were mixed in various combinations and stimulated with antigen Z in vitro. After three days anti-X antibody was measured. The results are shown in Table 2:
Table 2: In vitro anti-Z responses of different BALB/c and C57BL B + T cell mixtures
T cell source B cell source Anti?Z antibody
– BALB/c 4
– C57BL 2
BALB/c – 6
C57BL – 7
BALB/c BALB/c 6
C57BL BALB/c 260
BALB/c C57BL 3
C57BL C57BL 255
NB: In control cultures [not shown] where no antigen was added, no responses above 10 mcg/ml were observed regardless of cell input.
What do you conclude from Table 1 about the genetic relationship of IgH and the locus controlling the responder/non-responder phenotype? Why?
What do you further conclude from Table 2? Are these results consistent with the conclusions you drew from table 1? Why/why not?
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