Successful skin homografts in inbred chickens

Reduction in Animal Use 35 Years after Russell & Burch's Principles of Humane Experimental Technique

“Reduction” in animal use can be achieved by better experimental strategy and improved experimental design. In 1959, one strategy for discovering new drugs involved the random testing of thousands of chemicals in animal models of disease. This strategy was deplored by Russell & Burch in The Principles of Humane Experimental Technique (1959) as being inefficient and inhumane, and has now been almost completely superseded, following fundamental research resulting in an improved understanding of the mechanisms of drug action. Random screening is still done on a large scale, but by using in vitro methods.

Good experimental design involves the control of variation. In 1959, it was not clear whether isogenic (inbred or F1 hybrid) strains of mice and rats were more uniform than outbred stocks and whether they should therefore be used preferentially in bioassays. It is now generally accepted that F1 hybrids and inbred strains tend to be more uniform, but, as precision also depends on sensitivity, which is unpredictable, there is no general rule for choosing the best strain for a bioassay. Choice should be based on pilot studies. However, the use of more-uniform, specific pathogen-free animals, which were only just becoming available in 1959, has certainly reduced the number of animals which are used.

Other aspects of experimental design, such as the need to avoid bias, have a wide range of applicability; the importance of simplicity and the ability to calculate uncertainty are, apparently, not always appreciated by research scientists.

The concept of “reduction” has been useful in focusing attention on the need for improved experimental design. In the long-run, animal welfare legislation and improved training for research scientists should lead to improvements, not only in the way in which animals are kept, but also in the way in which experiments are planned and analysed.

Relationship of B blood group locus to skin allograft in chickens

Skin grafts were exchanged among 21 genotypic pairs of B blood group locus in the non-inbred chicks of White Leghorn at 5-7 days of age. The mean percentages of B locus compatible pairs were 94.7, 84.2 and 56.8 at the 11th, 15th and 19th days after grafting, respectively. These percentages of survival grafts were significantly higher than those of incompatible pairs. The effects of three B alleles were investigated but the differences of effects of them were not found in this experiment. Two of the prolonged survival grafts survived for 35 days after grafting and all of the incompatible grafts were rejected the 20th day after grafting. The results of skin graft provided evidence that the B blood group locus was a histocompatibility locus or closely linked to such a locus.

Histocompatible chicken inbred lines: homogeneities in the major histocompatibility complex antigens of the GSP, GSN/1, PNP/DO and BM-C inbred lines assessed by hemagglutination, mixed lymphocyte reaction and skin transplantation

Chicken inbred lines of the GSP, GSN/1, PNP/DO and BM-C have been established by selection of a specific allele at the B blood group locus (MHC B-G region) and other polymorphic loci through pedigree mating. To extend the potential of these inbred lines as experimental animals in Aves, we assessed the antigenic homogeneities of the MHC antigens by three immunological methods. Antigenic variations of red blood cells (RBCs) were surveyed in the inbred lines and a random-bred line (NG) derived from the Nagoya breed by using ten kinds of intact antisera produced in the inbred line of chickens against RBCs of a red junglefowl and hybrids. In the hemagglutination test, no individual variations were found within the inbred line at all, while all the ten antisera detected highly heterogeneous reactions in individuals of the NG. The reciprocal one-way mixed lymphocyte reactions gave constantly higher stimulation responses (P<0.01) between individual pairs from the inbred lines having different B alleles compared to pairs within the inbred line, while lower stimulation was observed between pairs of the GSP and GSN/1 inbred lines both having the B(21) allele. In reciprocal skin transplantation, the transplanted skingrafts within the inbred line and between individuals from the GSP and GSN/1 inbred lines survived more than 100 days, while all the skingrafts showed signs of rejection within 7 days among the inbred lines having different B alleles. The results obtained by the three practical methods coincidentally indicated that the individuals in the respective four inbred lines were histocompatible, and further, that the GSP and GSN/1 individuals were histocompatible.

Immunogenetics of the A-E alloantigen complex

The close linkage (0.5%) between the A and E erythrocyte alloantigen loci present a special challenge in the production of locus-specific typing antisera. The objective of the investigation was to determine immunogenetically the A-E haplotypes (genetically linked combinations of A and E antigens) existing in the locally maintained individuals of the New Hampshire (NH) and White Plymouth Rock (WR) breeds. The A and E alloantigens in these populations were identified using reference antisera previously produced in White Leghorns. A total of four A-E haplotypes were identified within each of the two breeds; A2E1, A6E2, A6E4, and A8E2 in WR and A2E1, A3E7, A7E4, and A8E2 in NH. Individuals of these two brown-egg breeds were backcrossed over several generations to a line of Ancona chickens homozygous at the A and E loci. Genetic segregation occurring over four generations resulted in nonrecombinant and recombinant progeny that were immunized reciprocally with the blood of siblings to raise antibodies reactive with the individual A and E antigens of the NH and WR stocks. The antisera resulting from the within-family alloimmunizations confirmed the haplotypes deduced in the WR and NH lines from the initial tests with the A and E reference antisera.

Ontogeny and expression of chicken A blood group antigens

Expression of chicken red blood cell (RBC) surface antigens was studied by using a monoclonal antibody (ISU-cA) specific for chicken A blood group antigens. Erythrocytes were examined from embryos of 3-18 days of incubation and from chicks at hatch up to 21 weeks of age. Specific antigens were detected on embryonic RBC surfaces by immunofluorescence as early as 3 days of incubation. Antigenic expression was examined by both haemagglutination and immunofluorescence and found to increase with age from embryos to mature birds. The antigen concentration on the cell surface was found to be affected by genotype; heterozygotes had an intermediate level of antigen between that of the two parental genotypes. These data confirm the co-dominance that is observed with most blood group antigens. Flow cytometric analysis allowed confirmation that the entire erythrocyte population gradually increased in antigenic expression over time, rather than having an antigen-negative subpopulation being replaced by a positive subpopulation.

Specificity in the immunosuppression induced by avian reticuloendotheliosis virus

Several parameters of the cellular and humoral immune responses of chickens infected with reticuloendotheliosis virus (REV-T), an avian defective acute leukemia virus, or with its helper virus, reticuloendotheliosis-associated virus (REV-A), were evaluated. Spleen cells from chickens infected with REV-T (REV-A) or REV-A exhibited depressed mixed lymphocyte and mitogen responses in vitro. Allograft rejection was delayed by 6 to 14 days in birds infected with REV-A. The specific antitumor cell immune response was also studied by a 51Cr-release cytotoxicity assay. Lymphocytes from chickens infected with low numbers of the REV-T-transformed cells exhibited significant levels of cytolytic reactivity against the 51Cr-labeled REV-T tumor cells in vitro. The mitogen response of lymphocytes from these injected birds was similar to that of uninjected chickens. In contrast, lymphocytes from chickens injected with higher numbers of REV-T-transformed cells exhibited suppressed mitogen reactivity and failed to develop detectable levels of cytotoxic activity directed against the REV-T tumor cells. These results suggest that the general depression of cellular immune competence which occurs during REV-T (REV-A) infection could contribute to the development of this acute leukemia by inhibiting the proliferation of cytotoxic cells directed against the tumor cell antigens. The cytotoxic effect observed after the injection of chickens with non-immunosuppressive levels of REV-T-transformed cells appears to be specific for the REV-T tumor cell antigens since cells transformed by Marek's disease virus or avian erythroblastosis virus were not lysed. In marked contrast, birds whose cellular immune responses were suppressed by infection with REV-A were capable of producing a humoral immune response to viral antigens. Detectable levels of viral antibody, however, did not appear until 12 to 15 days after REV-A infection. Since REV-T (REV-A) induced an acute leukemia resulting in death within 7 to 14 days, it appears unlikely that the ability of chickens to make antiviral antibody influences the development of lethal reticuloendotheliosis.

The allograft reaction as an index of genetic diversity in inbred chickens

The main purpose of the study was to use the skin allograft reaction as a possible biological tool to estimate genetic diversity (inbreeding) in a population and to determine the relative influence on the B locus blood group locus on variation in graft rejection. In chickens, the B locus is the major histocompatibility system. One outbred and five inbred lines were used in 12 skin grafting experiments. Graft exchange also were made between certain line crosses. The study was based on 2172 allografts performed on 712 chickens.Incompatibility of the B blood group locus accounted for 3/4 of the total variance in homograft rejection within lines. For the compatible allografts only, lines accounted for more than 90% of the total variation.Graft acceptance in terms of mean survival time (MST) was highest in the most highly inbred lines and lowest in the noninbred control. The regression of genetic diversity, as a function Wright's inbreeding coefficient, as a percentage of allograft rejection may be a useful biological index of genetic diversity.

Relationship of Blood Type to Histocompatibility in Chickens

Evidence shows that the B blood group locus in chickens, which controls red cell antigens, is associated with tolerance of skin homografts. Three other blood group loci studied did not show this effect.