Role of adherent cells in graft-versus-host-induced suppression of the humoral immune response.

Experiments were performed to investigate the role of adherent (A) cells in graft-versus-host (GVH)-induced immunosuppression. GVH reactions (GVHR) were induced in adult F1 hybrid mice by intravenous injections of parental lymphoid cells. Spleen cells (SC) from mice experiencing a GVHR (GVH mice) were stimulated with phytohaemagglutinin (PHA), concanavalin (Con A), and lipopolysaccharide (LPS). SC taken in the early phase of the GVHR (early GVHR) responded normally to LPS but did not respond to PHA and Con A. SC taken in an advanced phase of the GVHR (advanced GVHR) did not respond to PHA, Con A, or LPS. The influence of A cells from GVH mice (GVH-A cells) on the response of normal non-adherent cells to sheep erythrocytes (SRBC), PHA, and LPS was investigated. A cells from early GVHR, used in appropriate numbers, stimulated the responses to SRBC and to PHA; in excess they inhibited both responses. They had no effect on the response to LPS. A cells from advanced GVHR, even in low numbers, suppressed the responses to SRBC, PHA and LPS. The lymphoregulatory activities of GVH-A cells seemed to be mediated by soluble factors. The results indicate that the GVHR evokes complex non-specific regulatory interactions between A cells and lymphocytes.