Studies on lymphocyte subpopulations and the effect of age on immune competence in turkeys

We characterized the lymphocyte subpopulations and investigated the effect of age on cellular and humoral immunity, development of lymphoid organs, and the relative proportions of CD4⁺ and CD8⁺ cells in turkeys. The mitogenic responses of peripheral T cells were poorly developed at hatch but developed rapidly after hatch and reached adult levels by 2 weeks-of-age. The average percentage of CD4⁺ cells was 45, 29.8, and 26.3 in the thymi, peripheral blood, and spleens, respectively, in turkeys. The mean percentage of CD8⁺ cells in the thymi, peripheral blood, and spleens of turkeys was 53.8, 13.6, and 15.5, respectively. Age did not influence the relative proportions of CD4⁺ and CD8⁺ T cells in the spleens and peripheral blood of turkeys. The mean percentages of IgM⁺ cells in the bursae and spleens were 78.5 and 26.8, respectively. Day-old turkeys did not develop detectable antibodies to either thymus dependent or independent antigens. However, 2 week or older turkeys showed good humoral responses. Inoculation of BSA at hatch induced tolerance, whereas injection of SRBC did not. Analysis of relative organ weights of turkey lymphoid organs showed that spleens and thymi developed rapidly during the first week-of-age.