In vivo and in vitro effects of acute graft-versus-host serum in the rat.

Pooled serum from 6- to 8-week-old female Lewis x Brown Norwegian F1 hybrid (LBNF1) rats undergoing acute local graft-versus-host (GVH) reactions was found to have the ability, when compared with normal F1 serum, to increase node weight in a popliteal lymph node weight gain assay in syngeneic animals. Suspension of donor cells in normal F1 serum on one side and corresponding concentrations of GVH serum on the contralateral side resulted in an average increase in popliteal node weight of 28.8 per cent on the side receiving GVH serum. Of the 64 animals tested, 50 had larger nodes on the GVH serum side. This effect was not impaired by heating (56 C, 30 min) or by rapid freezing (-75 C) and thawing of the serum. Preinjection of the serum into the footpads 2 hr before donor cells also gave increased node weights as did injection of the serum i.p. In contrast, GVH serum was found to inhibit unidirectional mixed lymphocyte cultures of seven different allogeneic rat strain combinations, the inhibition ranging from 35 to 74 per cent. In addition, the blastogenic cell responses of three different strains to phytohemagglutinin P were inhibited between 45 and 77 per cent. The relationship between these two phenomena, in vivo increase in node weight and in vitro inhibition of blastogenesis, is not clear and is the object of further investigation.