B-CELL PRECURSORS IN EARLY CHICKEN EMBRYOS

Abstract

The ontogeny of B[bursa-derived]-cell precursors in chicken embryos from day 3 of incubation onwards was studied. Purified antibodies to chicken Ig[immunoglobulin]L, .gamma., .mu. and .alpha. chains were used in a sensitive indirect immunofluorescence assay on fixed cell smears and wax-embedded tissue sections. The location and morphology of Ig+ cells were determined in phase contrast or after histological staining. Lymphoid cells containing small amounts of cytoplasmic[c] Ig were found in 3 day and older embryonic yolk sac, 11 and 12 day blood, 11, 12 and 13 day bursal mesenchyme. cIg + large basophilic cells were first seen in 14 day bursal follicles. Cells apparently enter the embryonic bursa at different developmental stages. Some appear to be uncommitted stem cells, while others have already commenced B-cell maturation in an extra-bursal site.