Effects of anti-T lymphocyte serum on immunological reactivity and on the T cell area of the cloacal bursa in the chicken.

The effects of rabbit anti-chicken T-lymphocyte serum (RACTS) on the immune response in chickens stimulated either locally (per anum) or systemically (i.p.) with sheep red blood cells (SRBC; T-cell-dependent antigen) as well as on the morphological characteristics of the diffusely infiltrated area (DIA; T-cell region of the bursa) were studied. Antibody response to SRBC was measured by the serum anti-SRBC agglutination titres. In the DIA, the percentages of T cells, B cells and macrophages (MPS cells) were counted, and the different parameters of the post-capillary venules (PCVs) determined morphometrically. The response to SRBC was very significantly impaired in locally immunized chickens treated systemically with RACTS. In the DIA, the relative number of T cells was dramatically decreased, as was, although less drastically, that of MPS cells. In chickens immunized locally with SRBC, RACTS caused strong morphological alterations in the PCVs of the DIA; decrease in the diameter of the PCV and its lumen and flattening of the endothelial cells. The migration index did not significantly decrease due to the RACTS treatment. Following the systemic immunization with SRBC, no changes in the morphology of the PCVs attributable to the RACTS treatment could be observed. The present results give further support to the concept of the structural and functional analogy between the chicken cloacal bursa and the mammalian gut-associated lymphoid tissue (GALT) and the lymph nodes, thus strongly favouring the idea of the bursa functioning like a peripheral lymphatic organ.