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. On the other hand, B10 mice showed no antibody reactivity against A13 antigen. The antibody reactions against antigen A13 could be induced in B10 mice by immunization with the respective erythrocytes. In this case, the antibody activity was concentrated in the IgG fraction of the serum. After immunization of B10 mice, agglutinating antibodies against antigenic determinants of the Ea-B (MHC) system appeared, which were not detected in NMS.

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. Bursectomy influences the expression of this resistance to a lesser extent than thymectomy. The results indicate that resistance to the development of progressively growing tumours is of a complex nature, the individual components of the immune system are more or less important for its expression in different experimental models. Thus genetically defined animal models have become useful tools for studying carcinogenesis.

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. The different reactivity of the congenic chicken lines IA and IC, which are identical in the B complex (MHC) and differ only in erythrocyte antigens of the A blood group system, suggests that natural antibodies may also react with antigens other than the chicken MHC antigens. On the other hand, normal sera from chickens of inbred lines reacted with all erythrocytes of the different mouse strains tested.

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.