Further Studies in Tissue Homotransplantation in Cattle

The present contribution presents a sequel to our previous investigations into problems which arose when attempts were made to use skin grafting to differentiate between monozygotic and dizygotic twins in cattle. In each of three trials grafts from a dam elicited similar reactions when transplanted to each of her one-egg twin offspring. On the basis of this finding the asymmetry of response which the majority of two-egg twins show towards grafts from their dam may be taken as evidence of their dizygotic origin.It has been shown that mutual graft exchange between unlike-sexed twins can be used as a reliable method for distinguishing reproductively normal females from freemartins. The complete success of this method provides strong evidence that homograft tolerance and the freemartin condition have a common anatomical origin.Grafts from a dam to her tetrazygotic offspring lived for upwards of 70 days, whereas grafts from a dam to her offspring of single birth rarely live for as long as 14 days. It is argued that this great prolongation in the life of their grafts is the outcome of the quadruplets having previously exchanged cells in foetal life through anastomoses of their circulations. Each must be incapable of reacting against a very wide spectrum of antigens since it will accept grafts from all its brothers and sisters.Evidence is presented which suggests that cells from her foetus not infrequently gain access to a dam and sensitize her to subsequent grafts of her offspring’s skin. A first pregnancy may be sufficient to elicit this sensitization. On the other hand, if maternal cells gain access to the foetus, this must occur very rarely for in none of seventeen calves tested with grafts of their dam’s skin was there the slightest evidence that they were tolerant.New-born calves react as vigorously as adult cattle against homografts, even when they have not received colostrum. Since new-born calves possess no serum globulins, including antibodies, this provides strong evidence that immune globulins play no essential part in the homograft reaction.