Mouse sera contain "natural" antibodies directed exclusively against polymorphic--non-histocompatibility--antigens of the chicken Ea- A blood group system.

Natural agglutinating antibodies in normal sera from A and B10 mice react exclusively with antigenic determinants of the polymorphic Ea-A blood group system (a non-histocompatibility system) of the chicken. Agglutinating activity of these "natural" antibodies, which was demonstrated in the IgM fraction of the serum, did not correlate with the cytotoxic activity against chicken cells in A mice compared to B10 mice. "Natural" agglutinating antibodies against antigens A13 and A14 present in chickens of congenic lines were demonstrated in NMS from A mice.

Different importance of primary lymphoid organs for Rous sarcoma regression in inbred lines of chickens.

Resistance to progressive growth of tumours induced by Rous sarcoma virus is controlled mainly by genes linked to the B complex (the major histocompatibility complex) of the chicken. The effect of thymectomy and bursectomy on this resistance was studied in chickens from highly inbred lines and their F1 hybrids which differ by the genotype at the B complex and by the degree of genetically controlled resistance or susceptibility. The results show that thymectomy has considerable effect on growth of RSV-induced tumours in the CB line genetically resistant to progressive Rous sarcoma growth and little effect in (CB X IC)F1 (also genetically resistant) and (CC X IC)F1 (intermediate responders to RSV) hybrid chickens.

Interstrain differences in the reactivity of normal mouse sera against erythrocyte surface antigens of inbred chicken lines.

Normal mouse sera from non-immunized individuals of different strains gave high titres of "natural" antibodies which agglutinated RBC's of different inbred lines of chickens. Normal mouse sera of A strain and its congenic lines agglutinated RBC's of all chicken lines whereas normal sera of B10 strain and its congenic lines did not react with RBC's of Iowa A line. Normal sera of other mouse strains behaved similarly.

Failure to confirm the role of immunological tolerance to B (MHC) alloantigens in the growth of RSV-induced tumours in chickens.

Chickens of the inbred "regressor" line CB (B12/B12) were made tolerant to the B13 (MHC) alloantigen of the congenic "progressor" line CC and then challenged with Prague strain of Rous sarcoma virus of subgroup C. No changes in tumour growth between tolerant and control groups were observed. These results suggest that there is no cross-reactivity between B13 alloantigen and RSV-induced tumour antigens.