Production and traffic of B lymphocytes in the extracortical central area of the guinea pig thymus.

Lymphocytes in the stroma and lymphatics of the extra-cortical central area (ECCA) of the guinea pig thymus have been studied with light microscopy, quantitative microscopy, colchicin-induced mitotic arrest, EA (IgG) and EA (IgM) C adherence, surface immunoglobulins (Ig total, IgM, IgG), alkaline phosphatase activity and the effect of cyclophosphamide administration. The results suggest, that AP-positive, SIg-positive EAC-negative lymphocytes in the ECCA proliferate and maturate into AP-negative, SIg-positive, EAC-positive lymphocytes. The latter leave the thymus through the lymphatics. Calculations show that daily 8-9 X 10(6) B lymphocytes are produced in the ECCA and leave this area through the lymphatics. As this number is more than 10% of the number of T cells which daily leave the thymus, we conclude that in the ECCA a considerable number of B lymphocytes is produced.