A study of the role of macrophages in the graft-versus-host reaction

Resting PEC and fractions of spleen cells adherent to nylon wool (NASC) or polystyrene (PASC) from A/Ph mice evoke a weak regional GVHR or no systemic GVHR in (B10 X A/Ph)F1 hybrids. Blockage of macrophages in vivo by silica or silica gels or removal in vitro of cells phagocytosing iron particles did not change GVH reactivity of A/Ph spleen cells. Addition of PEC or NASC from A/Ph mice to the A/Ph spleen cell suspension somewhat suppressed regional GVHR but enhanced systemic GVHR. Addition of PASC from A/Ph mice, conversely, enhanced regional GVHR and suppressed systemic GVHR. Repeated administration of silica and silica gel to the recipients suppressed regional GVHR; a single dose of silica was most effective at suppression when given one day before the cells. Systemic GVHR was not influenced by this treatment of the recipients. The results indicate that macrophages do not directly induce a GVHR, but they serve as important targets in regional GVHR. In regional and systemic GVHR macrophages perform regulatory functions. Macrophages of donor origin may modify both types of GVHR significantly, depending on the source and type of macrophages and the treatment of donors.