Morphometric analysis of CD4+, CD8+, and γδ+ T-lymphocytes in lymph nodes of cattle vaccinated with Brucella abortus strains RB51 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 injected subcutaneously in the axillary area with 1×1010 live B. abortus strain RB51 (SRB51, n = 12) or strain 19 (S19, n = 6) suspended in 2 ml of saline. Six control heifers were injected with sterile saline. Lymph nodes were collected at 1, 2, 4, 6, 10 and 12 weeks postvaccination. 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 γδ (IL-A29) bovine T-cell surface antigen and processed for immunoperoxidase staining. Numbers of stained lymphocytes in randomly selected fields were calculated using image-analysis software. There were no significant differences in the number (P = 0.07) or relative proportions (P = 0.22) of CD4+, CD8+, and γδ+ 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 closely grouped and the γδ+ cells had the most widely scattered distribution, regardless of vaccination status. The results support other studies indicating lymphocyte depletion is not a sequela of infection with B. abortus vaccine strains given to conventionally reared cattle.