Liver sinusoidal lining cells express class II major histocompatibility antigens but are poor stimulators of fresh allogeneic T lymphocytes.

Guinea pig liver sinusoidal lining cells (LSLC), a mixture of Kupffer cells (KC) and sinusoidal endothelial cells (EC), were examined for their capacity to function as antigen-presenting cells (APC). LSLC were extremely poor stimulators of freshly isolated allogeneic T lymphocytes even though a large number of them expressed class II major histocompatibility complex (MHC) antigens (Ia). This deficiency could not be explained by a lack of soluble factor production by LSLC, because an interleukin 1-containing macrophage (M phi) supernatant could not restore the capacity of LSLC to stimulate allogeneic T cells. Moreover, LSLC were able to promote mitogen-induced proliferation of accessory cell-depleted T lymphocytes. No evidence of suppression was apparent in experiments in which LSLC were added to cultures of T cells stimulated by allogeneic peritoneal exudate M phi (PEM). The Ia expressed by LSLC was functional because they were able to stimulate an alloreactive T cell line. When LSLC were mixed and co-cultured with either PEM syngeneic to the responding lymphocytes or Ia-negative fibroblasts, the allostimulatory ability of LSLC was greatly augmented. In contrast, the addition of mitogen-activated T cell supernatants had only a minimal effect on the capacity of LSLC to stimulate allogeneic T cells. The data suggest that LSLC lack a biologic property that is necessary for recognition of class II MHC determinants by fresh but not primed allogeneic T cells and that is not required to support T cell activation induced by nonspecific mitogenic lectins. These findings may be important in understanding the reason that antigen introduced into the portal blood appears not to initiate an immune response.