Robert G. Tissot

Histocompatibility in the rabbit. Linkage between RL-A, MLC, and the He blood group loci.

Rabbits from three inbred lines, all descended from a common ancestor, have very similar, but distinct, RL-A alleles. Leukocytes from rabbits homozygous for these similar alleles do not cross stimulate in the mixed lymphocyte culture (MLC) test. Unrelated, noninbred, RL-A-identical rabbits, produced by genetic crosses of known genotypes, also fail to cross stimulate in the MLC test. Thus, the locus controlling the MLC response and the RL-A locus are closely linked, but not identical. The RL-A-MLC histocompatibility complex is also linked to a third locus, the He blood group locus.

Histocompatibility in the rabbit: genetic control of rabbit mixed leukocyte culture reactivity.

SUMMARY As a part of our development of the rabbit as a model system for transplantation, we investigated the genetic factors influencing the reaction levels obtained in rabbit mixed leukocyte cultures. Inbreeding strains and noninbreeding rabbits that were serologically characterized for their major histocompatibility complex (MHC) were compared for their levels of response in reciprocal unidirectional semimicro mixed leukocyte cultures. Tests between inbreeding or noninbred rabbits that were identical for their serological determinants showed weak or no cross-stimulation; this confirmed our earlier findings which show that the mixed leukocyte culture response in the rabbit is governed by a locus (RLD) which is an integral part of the major histocompatibility complex. Cultures of cells from rabbits with distinct MHC haplotypes demonstrate varying levels of response which, in one-way reactions, is controlled primarily by the particular allelic combinations of the stimulating and responding cells. By comparing the responses of rabbits from two separate sublines which were identical for their MHC serological and lymphocyte-defined determinants, we have found evidence for a locus independent of the MHC, which influences the magnitude of the response to RLD-mismatched stimulators. Weak reactions have been observed between certain donor combinations that have identical RLA haplotypes; these may represent the contribution of minor loci to the reaction levels. Mixed leukocyte reactions between homozygotes having nine distinct MHC haplotypes show that these haplotypes may be arranged into mutually nonreactive subsets. This suggests a restricted polymorphism of the RLD alleles, compared to the serological polymorphism in our colony.

The effect of the RL-A locus and the NLC locus on graft survival in the rabbit.

Skin grafts exchanged between RL-A-mismatched and MLC-mismatched rabbits are not maintained for more than 12 days. RL-A-identical MLC-matched grafts in unrelated rabbits do not survive for a significantly prolonged period of time over mismatched controls, but as the degree of relationship between donor and recipient increases, graft survival time in RL-A-identical MLC-matched rabbits increases significantly. Treatment with 6-mercaptopurine produces only a slight prolongation of graft survival time in RL-A- and MLC-mismatched rabbits; however, 6-mercaptopurine treatment produces a very significant increase in graft survival time in RL-A-identical MLC-matched animals. Grafts exchanged between RL-A-mismatched and MLC-matched rabbits treated with 6-mercaptopurine do not survive longer than RL-A- and MLC-mismatched controls.

Stable chimerism induced in noninbred rabbits by neonatal injection of spleen cells from allotype-suppressed adult donors. I. Replacement of hemopoietic tissue by donor cells.

In the course of experiments designed to demonstrate an active mechanism of allotype suppression in rabbits, spleen cells from adult donors were transferred to newborn recipients. Among 23 rabbits that received injections, 4 stable chimeras were formed, as determined by the production of serum immunoglobulins marked with light and heavy chain allotypes. The other rabbits that survived the immediate postinjection period displayed a temporary chimeric state lasting up to several weeks, after which they either succumbed to graft-versus-host disease or rejected the donor cells. One chimeric animal was apparently repopulated by the hemopoietic cells of the donors spleen. Insofar as could be determined, the recipients blood cells became phenotypically identical to those of the donor. This condition manifested itself as a loss of the recipient gene products associated with both lymphocytes and erythrocytes, accompanied by a seemingly total replacement with those of the donor.

Identification of two Ia-like alloantigens on rabbit B lymphocytes

Alloimmunizations with rabbit lymphoid cells have resulted in the identification of two cell-surface alloantigens, Ia1 and Ia2. These antigens reside on nearly all B cells; few, if any thymus cells or T cells of mesenteric lymph nodes bear these antigens. Genetic studies showed that Ia1 and Ia2 molecules appear to be controlled by allelic genes at a locus closely linked to the MHC. Immunochemical analyses revealed that Ia1 and Ia2 are glycoproteins and that each is composed of two polypeptide chains of molecular weights of 28 000 and 30 000–32 000. Thus, the alloantigens identified by these two antisera appear to be Ia-like molecules.

Factors affecting natural antiallotype antibody production in rabbits

Since not all rabbits that have receivedb locus-incompatible antigens from the mother respond with natural antiallotype antibody, various factors were studied to determine their role in the expression or nonexpression of antibody production in the individual rabbit. It was found that the mother-offspring allotype relationship is important in determining the probability that a given individual will respond to maternally derived allotype differences, and that the ability to respond is under genetic control. The genetic basis appears to be polygenie with the response status of a given animal determined by a threshold of response-positive genes needed for response. A greater number of response-positive genes seems to be required if there is an antigenic relationship between the incompatibleb-locus antigen from the mother and the individuals ownb-locus antigens.

Platelet survival test. An accurate prediction of hyperacute rejection of renal allografts in rabbits.

SUMMARY The platelet survival test (PST) was evaluated as a means of predicting hyperacute renal allograft rejection. Renal allografts were performed in 12 control and 22 actively preimmunized animals within 1 week of completing immunization. Immunological reactivity assessed immediately prior to renal transplantation was accurately measured by the PST. No hyperacute rejection developed in the control animals or in 10 animals with a slight reduction of platelet survival. Of 12 animals with a moderate or severe reduction of platelet survival, gross and clinical signs of hyperacute rejection were present in 10, and histological evidence of hyperacute rejection was present in 7. Presence or absence of cytotoxic antibody was poorly correlated with eventual outcome. Hyperacute rejection developed in only 1 of 5 animals with a moderate or strong cytotoxic antibody titer; 2 animals with hyperacute rejection had no detectable cytotoxic antibody.

Homozygous cell typing for the rabbit RLA-D antigens in animals from commercial breeders

We have previously reported that several of theRLA haplotypes of our rabbits have anRLA-D allele in common, i. e., they fail to cross stimulate in the MLC test. To investigate the possibility that these haplotypes originated in unrelated animals, a panel of homozygous rabbits was selected to partially characterize noninbred rabbits from five commercial sources for their alleles at theRLA-D locus. In the 47 rabbits tested, 4 homozygous animals and 12 heterozygous animals were detected with the four alleles chosen for typing. At least two independent pairs of rabbits shared identicalRLA-D genotypes. Our results indicate that theRLA-D locus is not extremely polymorphic and that rabbits cannot be assumed to be completely mismatched for theRLA complex simply because they are from different breeds or from independent suppliers.

Histocompatibility in the rabbit. The effect of imbreeding on skin graft survival time.

SUMMARY Skin grafts were exchanged between siblings from 16 inbreeding lines of rabbits. Progressive inbreeding and genome fixation through 12 generations of brother ± sister matings does not produce a concomitant increase in graft survival time but instead produces a heterogenous response reflecting the residual segregation of individual histocompatibility loci. Grafts exchanged between RL-A incompatible siblings were not maintained for more than 12 days, regardless of the degree of inbreeding. The frequency distributions of the survival times of grafts exchanged between animals from all inbreeding lines from each generation, F5 through F8, agree best with the expected values calculated by assuming that 17 independent histocompatibility loci, with 95% confidence limits of 11 and 28 loci, must be matched to assure acceptance of skin grafts for 60 days or more. However, in animals from line Sh5b, only 3 significant histocompatibility loci appear to be segregating. Two of the significant histocompatibility loci segregating in line Sh5b have not been identified; the third significant locus is either the Hg blood group locus or is linked to the Hg locus. Established loci that remain polymorphic during intensive inbreeding may be important in the development of a model transplantation system; as inbreeding progresses these established loci may be markers for histocompatiblity loci that have a significant effect on allograft survival time.

Histocompatibility matching in poor-prognosis penetrating keratoplasty.

Rabbits were haplotyped for the major rabbit leukocyte‐locus A (RL‐A locus), which is analogous to the human leukocyte‐locus A (HL‐A locus). The rabbits were divided into five groups, and the groups were arranged to provide a controlled experimental setting. Standardized alkali burns were induced in selected groups to produce heavy vascularization of the corneal bed.