ONTOGENY OF T-CELLS, B-CELLS AND MONOCYTES IN THE BOVINE FETUS

Abstract

The ontogeny of lymphocyte subpopulations and monocytes was studied in developing bovine fetuses. Bovine fetuses (54) ranging in age from 3-9 mo. of gestation were collected and examined for the presence of thymus-derived (T lymphocytes), bone marrow-derived (B lymphocytes) and phagocytic (macrophage) cells from thymus, spleen and peripheral blood. Detection of the cells expressing T lymphocyte surface markers was done using a modified sheep red blood cell rosette assay. Lymphocytes bearing surface immunoglobulin (sIg) were detected by staining with a fluoresceinated rabbit antibody prepared against bovine IgG. The procedure used for detecting monocytes was a latex bead phagocytic assay. In the thymus, the percentage of T lymphocytes was relatively constant throughout gestation at approximately 60-70%, with B lymphocytes remaining at about 1%, whereas the phagocytic cells showed an increase from 1% at 3 mo. to .apprx. 8% at term. The spleen showed an increasing percentage of T lymphocytes, from 11% at 3 mo. to 40% at term, whereas the percentage of B lymphocytes remained consistent at about 2-3% from 3 mo. until term. The percentage of monocytes increased from 1% at 3 mo. to over 20% at 9 mo. Peripheral blood T lymphocytes increased steadily from .apprx. 1% at 3 mo. to 45% at term. B lymphocyte levels remained low, about 1%, throughout gestation, whereas monocytes increased from 1% at 3 mo. to 5% at 9 mo.