MECHANISM OF IMMUNO-INHIBITION BY ARACHIDONIC AND LINOLEIC-ACID - EFFECTS ON LYMPHOID AND RETICULOENDOTHELIAL SYSTEMS

S.c. injection with certain polyunsaturated fatty acids (PUFA), in particular linoleic acid (C18:2), was recently shown to prolong the toxic responses by isolated spleen cells. In this study, changes in the lymphoid system and RES were examined in grafted and ungrafted mice treated according to the schedules which prolong allograft survival. Many of the changes in the lymphoid system and RES which can be produced by allografting could also produced in ungrafted animals by PUFA treatment. These changes included increased 125IUdR uptake by spleen, lymph nodes and bone marrow; increased spleen and lymph node wt; increased proportion of red pulp and granulocyte precursors in the spleen; and RES activation as shown by an increased rate of C clearance. The combined effects of allografting and C18:2 on peripheral lymph node wt were greater than the effect of either treatment alone, but fell short of the sum of both treatments. Allografting increased 125IUdR uptake/unit organ wt, in the peripheral lymph nodes, bone marrow, thymus and spleen. When allografted animals were C18:2 treated, this increase was considerably reduced, uptake being little different from that in C18:2 treated ungrafted controls. The number of .THETA.-positive cells in the spleen was markedly increased by a tumor allograft, but such an increase could not be seen in allografted animals when treated with C18:2. While prolonged C18:2 treatment led to destructive changes in the spleen, immunoinhibition could still be demonstrated after shorter treatments with C18:2 when no gross histological evidence for tissue destruction was apparent. Partial reversibility of inhibition of cytotoxic activity of isolated spleen cells could be demonstrated when treatment was discontinued.