Study of the thymic‐derived or ‐independent nature of mouse spleen cells induced to proliferate in culture by various mitogens and antigens

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Abstract
The nature of mouse lymphoid cells induced to proliferate in vitro by a number of stimulating agents has been explored by 1) karyotypic analysis of the mitoses observed in stimulated spleen cell cultures (arrested on sequential days) of chimaeras bearing chromosomally marked T cells; 2) comparison between the response in DNA synthesis of total spleen cells and of spleen cells depleted of thymus‐dependent lymphocytes by treatment with anti‐MSLA (anti‐mouse‐specific lymphocyte antigen) + C, and 3) study of the response of cortisone‐resistant thymocytes (CRT) to some of these agents. Pokeweed mitogen stimulated both B and T cells equally and simultaneously. Rabbit anti‐mouse Ig induced moderate proliferation of B cells exclusively. The response to lipopolysaccharide was entirely B cell‐dependent, but evidence was found of some T cell proliferation following or accompanying the stimulation of B cells. A similar observation was made in the case of “primary” or “secondary” in vitro response to bacteriophage T4. Good stimulation with sheep red blood cell stromas or mitogen‐treated xenogenic spleen cells were observed only in cultures from primed animals, and consisted of a mixed B and T cell proliferation with a majority of B mitoses, even at the earlier stages of the response. That this “secondary” response was not totally T cell‐dependent was suggested by the observation of a stimulatory effect of these antigens on T‐depleted spleen cell cultures which were found in parallel experiments to be totally unresponsive to PHA. Finally, using chimeric mice treated in vivo with vinblastine prior to establishment of the spleen cell cultures, evidence was obtained that part of the B cells stimulated to divide in vitro by several of these mitogens belong to a rapidly dividing cell population in vivo.