40
(both populations capable of responding) at 22C and 32C. Cultures
were initiated with 0.25 x 10^ lymphocytes from each donor fish per
culture well (0.5 x 10^ cells total). Controls in mitogen stimulation
studies for each fish also served as controls for mixed lymphocyte
cultures.
Four of ten two-way mixed lymphocyte cultures exhibited statis
tically significant responses (p < 0.05) and are presented in Table 6.
Significant responses were only obtained at 32C thus mimicking re
sponsiveness to PHA and Con A in temperature sensitivity. Furthermore,
these studies have indicated that maximal stimulation (not shown) in
the mixed lymphocyte cultures occurred at seven days. In this experi
ment all six bluegills studied had significant mitogenic responses,
indicating there is no direct correlation between PHA and LPS responsive
ness and the ability to respond to a mixed lymphocyte culture.
Evidence for Different Populations of Bluegill Lymphocytes
Golub (50) has demonstrated that rabbit anti-mouse brain cross re
acts with mouse thymocytes due to a common antigen on both brain and

thymocytes. In an attempt to elicit antiserum capable of recognizing
antigenic surface determinants on bluegill lymphocytes a rabbit was hy-
perimmunized with bluegill brain homogenates following Golub's immuniza
tion procedures. To determine the specificity of this rabbit anti-brain
serum for bluegill anterior kidney lymphocytes, cells were incubated
with the rabbit serum and guinea pig serum. After appropriate incuba
tion and washing only about 30% of the original number of cells remained
viable (as determined by trypan blue exclusion) in contrast to 100%