Difference in genesis between antigen-induced IgM antibody-forming cells and B-cell mitogen-induced IgM antibody-forming cells in mouse spleen cell cultures.

To determine the mechanisms in the triggering of thymus-independent lymphocytes (B cells) for development into antibody-forming cells (AFC), genesis of IgM AFC elicited polyclonally by nonspecific stimulation with B-cell mitogen, such as nystatin and bacterial lipopolysaccharide, was compared with that of IgM AFC specifically elicited by antigenic stimulation, using mouse spleen cell cultures as an experimental system and sheep erythrocytes (SRBC) as a test antigen. Considering that differentiation and proliferation are necessary cellular events for precursor B cells to develop into AFC, the effect of different antimetabolic agents on the generation of each type of AFC in spleen cell cultures was examined. The generation of anti-SRBC IgM hemolysin plaque-forming cells (PFC) in B-cell mitogen-stimulated spleen cell cultures was found to be less susceptible to X-irradiation or mitomycin C than that in the SRBC-stimulated cultures. These apparently paradoxical results were affiirmed using colcemid as an inhibitor of cell mitosis and hydroxyurea (HU) as an inhibitor of cellular DNA synthesis. Thus, when spleen cell cultures responding to either SRBC or B-cell mitogen were exposed to colcemid or HU during a period from 2 days to 3 days after the stimulation, the exponential generation of anti-SRBC IgM PFC in the cultures responding to SRBC was completely halted, whereas that in the cultures responding to B-cell mitogen was not. Furthermore, N⁶, O^2′ -dibutyryl adenosine 3′, 5′ -cyclic monophosphoric acid was found to halt the exponential generation of antigen-induced anti-SRBC IgM PFC but not that of the B-cell mitogen-induced anti-SRBC IgM PFC. From these results it was suggested that B-cell mitogen might stimulate precursor Bμ cells at a late stage in the differentiative pathway to develop into AFC without cell division, and that antigenic stimulation might stimulate relatively primitive precursor Bμ cells to proliferate and then differentiate into AFC. Based on this idea, mechanisms in the triggering of B-cell activation are discussed.     

Immunohistochemical study of the accumulation of antibody-forming cells in the lungs following intrapulmonary and subcutaneous administration of apneumotropic antigen]

Accumulation of the antibody-synthesizing cells in the lungs of guinea pigs in intratracheal and subcutaneous immunization was studied on a model of a complete typhoid bacilli antigen by means of Coons' method. Antibody-forming cells located in the interalveolar septi and in the peribronchial and perivascular connective tissue appeared with both method of the apneumotropic antigen administration. More of these cells accumulated in intrapulmonary application of the antigen. Repeated immunization by any method also led to the increase of their amount. The problem on the role played by the lungs in the immunogenesis is discussed.     

Growth and senescence of antibody-forming cells

Studies were performed on the capacity of mice for hemagglutinating antibody production throughout their life-span. An in vivo culture method was used for assessment of primary and secondary antibody-forming potentials of spleen cells of mice ranging in age from 1 to 130 weeks. There was a marked growth of potential for antibody formation during neonatal and juvenile life followed by a gradual decline in potential with advancing age. It was possible to show that the changes in potential were principally due to changes in the number of competent progenitor cells and not to changes in their performance. Death of very old animals was correlated with decline in number of immunologically competent progenitor cells. The decay in number of progenitor cells during aging of mice was random. Loss of progenitor cells was not entirely attributable to either generative failure of the pool of progenitor cells or the capacity of the milieu of the animal to support such cells. Thus, spleen cells from aged animals displayed increasing capacity for primary antibody formation during a 3-week period of culture in young, irradiated mice; identical cultures in old, irradiated recipients failed in respect to growth of primary antibody-forming potential. Progressive imparirment of the milieu of aging animals was suggested by the fact that spleen cells from very old animals were “toxic” when infused into lightly irradiated recipients which were themselves of advanced age but far short of the senescent phase of their life-span. These results lead to the argument that senescence may be, to a major degree, the result of progressive loss of progenitor, or “stem,” cells which are normally utilized to replace terminally differentiated, dying cells.