CELLULAR AND MOLECULAR ASPECTS OF IMMUNOLOGIC UNRESPONSIVENESS TO SHIGELLA PARADYSENTERIAE ANTIGENS*

Germinal-center cell proliferation in response to T-independent antigens: a stathmokinetic, morphometric and immunohistochemical study in vivo

Although the nature of the germinal center reaction during responses to T-dependent antigens has been well documented, much less is known regarding the relationship between germinal centers and T-independent antigens. In this study, germinal-center cell proliferation was determined at specific time points in spleens of C3H/HeN mice following immunization with either the type-1, T-independent antigen dinitrophenol-lipopolysaccharide (DNP-LPS), or the type-2, T-independent antigen DNP-Ficoll. A stathmokinetic technique was employed to assess proliferation in terms of germinal center cell birth rate and morphometry was used to measure actual growth and regression of the germinal center cell population. An estimate of the absolute rate of germinal-center (GC) cell proliferation was derived from these two values. In addition, immunohistochemistry was performed to correlate changes in GC cell proliferation with the presence or absence of antigen within GC. Following immunization with both antigens, there was an initial reduction of proliferation within pre-existing germinal centers which manifested as either GC dissociation (DNP-LPS) or a suppression of birth rates (DNP-Ficoll). This was followed by a period of increased GC cell proliferation in animals immunized with DNP-LPS, but not in those exposed to DNP-Ficoll. GC cell proliferation was then measured in mice treated with cyclosporin A from 1 day before to 2 days after immunization with DNP-LPS. In these animals, the expected increase in GC cell birth rates did not take place. Immunohistochemistry showed that DNP-Ficoll and DNP-LPS were present in GC from 1 day after immunization until the end of the experiment on day 7. Treatment with cyclosporin A did not affect the deposition of DNP-LPS in GC. These results show that only some T-independent antigens are able to stimulate GC cell proliferation, and we propose that this is related to their ability to recruit precursors of GC B cells into the GC reaction. In addition, the results indicate that GC proliferation seen in response to a so-called T-independent antigen is at least partly driven by T cell-derived cytokines.

Localization of intravenously injected lipopolysaccharide (LPS) in the spleen of the mouse. An immunoperoxidase and histochemical study

In earlier studies we investigated the in vivo effects of lipopolysaccharide (LPS) on lymphoid and non-lymphoid cells in the mouse spleen. In order to find out whether LPS localizes in and/or on cells that are affected by this compound, the aim of the present study was to investigate the localization of intravenously injected LPS in the mouse spleen using an immunoperoxidase technique. At different time points after injection, the localization of LPS is demonstrated and LPS-containing cells are characterized. Most of the injected LPS has been taken up by marginal zone macrophages at 2 h after its administration whereas macrophages in the red pulp and at the periphery of the white pulp (marginal metallophils) have ingested less LPS. In the periarteriolar lymphocyte sheath, LPS is concentrated in a large number of acid phosphatase-negative, Ia-positive, large branched cells which were suggested to represent interdigitating cells. Moreover an extracellular dendritic localization pattern of LPS is demonstrated in the corona and central parts of the follicles at different time intervals after its injection. The significance of the localization pattern of LPS in the mouse spleen is discussed.