MORPHOMETRIC ANALYSIS OF CD4(+), CD8(+), AND GAMMA DELTA(+) T-LYMPHOCYTES IN LYMPH-NODES OF CATTLE VACCINATED WITH BRUCELLA-ABORTUS STRAINSRB51 AND 19/

T-lymphocyte subpopulations were examined in vivo by computer-assisted morphometry of superficial cervical lymph nodes of cattle vaccinated with Brucella abortus. Twenty-four 8-month-old Hereford heifers were i njected subcutaneously in the axillary area with 1 X 10(10) live B. ab ortus strain RB51 (SRB51, n = 12) or strain 19 (S19, n = 6) suspended in 2 mi of saline. Six control heifers were injected with sterile sali ne. Lymph nodes were collected at 1, 2, 4, 6, 10 and 12 weeks postvacc ination. Both SRB51 and S19 were cultured from lymph nodes, but SRB51 persisted for a longer period after vaccination (10 weeks) than S19 (6 weeks). Cryostat sections were incubated with monoclonal antibody to CD4 (IL-A11), CD8 (IL-A51), or gamma/delta (IL-A29) bovine T-cell surf ace antigen and processed for immunoperoxidase staining. Numbers of st ained lymphocytes in randomly selected fields were calculated using im age-analysis software. There were no significant differences in the nu mber (P = 0.07) or relative proportions (P = 0.22) of CD4(+), CD8(+), and gamma/delta(+) lymphocytes in SRB51, S19, and control lymph nodes. There was a statistically significant difference in the distribution of the three T-cell subsets (P = 0.001). The CD4(+) cells were most cl osely grouped and the gamma/delta(+) cells had the most widely scatter ed distribution, regardless of vaccination status. The results support other studies indicating lymphocyte depletion is not a sequela of inf ection with B. abortus vaccine strains given to conventionally reared cattle.