q2

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?