Joy Palm

Genetic Control of Susceptibility to Experimental Allergic Encephalomyelitis in Rats

Rats of the inbred strains Lewis and DA are highly susceptible to the induction of experimental allergic encephalomyelitis (EAE) while Brown Norway rats are resistant to this disease. Evidence has been obtained which suggests that a single dominant gene is associated with susceptibility to EAE. The locus controlling EAE susceptibility is closely linked to the Ag-B histocompatibility locus but is not identical to it.

Interrelationships of inbred rat strains with respect to Ag-B and non-Ag-B antigens.

SUMMARY In the rat, a minimum of four genetic loci, Ag-A, Ag-B, Ag-C, and Ag-B, determine cellular antigens with different properties of intraspecific immunogenicity, tissue distributions, and histocompatibility associations. Eighteen inbred strains have been classified for the presence of specific alleles. A number of strains were found to exhibit the same antigen at the important Ag-B histocompatibility locus. The historical facts available for each strain suggest that the most probable explanations for this situation are: (1) multiple fixation of the same allele by inbreeding from heterogeneous stocks having common ancestry and (2) long-term stability at the Ag-B locus within inbred strains.

Immunogenetic analysis of Ag-B histocompatibility antigens in rats.

SUMMARY Rat alloantisera from reciprocal immunizations with eight combinations of inbred strains have been subjected to absorption analysis for the presence of Ag-B and non- Ag-B antibodies. Reagents detecting 12 Ag-B specificities were denned and used to characterize six alleles (Ag-Bl-Ag-B6) for which the prototype strains were designated as Lewis, Wistar/Furth, BN, DA, AUG-28807, and Buffalo, respectively. In addition to various cross reactive patterns, the Ag-B antigens determined by each of the six alleles were found to possess distinctive specificities, and these factors were incorporated into the Ag-B allelic terminology. Linkage tests established the independence of the Ag-B genes from those at the Ag-C locus and at four loci which determine coat characteristics. The serological interrelationships of the various Ag-B antigens are discussed in terms of both strain ancestry and possible relevance to interstrain immunogenicity.

Mixed Leukocyte Reactions and Histocompatibility in Rats

Mixed leukocyte culture tests have been carried out on two hetero geneous but genetically defined backcross populations of rats to determine whether the reactions observed can provide the basis for histocompatibility matching. The experiments were designed so that only-one-way reactions could occur. Only when the donors of individual leukocyte mixtures differed at the important Ag-B histocompatibility locus was there any in vitro reactivity, and differences at this locus were invariably associated with the prompt rejection of skin homografts. Determination of compatibility at this locus proved to be important in that it facilitated the prolongation of survival of skin homografts by immunosuppressive therapy.

Serum esterase genetics in rats: Two new alleles at Es-2, a new esterase regulated by hormonal factors, and linkage of these loci to the Ag-C blood group locus

Two new alleles at the Es-2 locus are described which determine electrophoretic variants of serum esterases of rats. A new esterase protein is described which is detectable in sera of sexually mature females of the appropriate genotype. Evidence is presented for genetic linkage between the Ag-C blood group locus and Es-1, Es-2, and the locus controlling the sex-influenced protein. Since the Ea-1 blood group locus of mice is linked to four esterase loci, it is suggested that Ag-C is the rat homologue of the mouse Ea-1 locus.

IDENTIFICATION OF A SINGLE STRONG HISTOCOMPATIBILITY LOCUS IN THE RAT BY NORMAL SPLEEN‐CELL TRANSFER*

When adequate doses of immunologically competent cells are transferred from an adult donor into a host that possesses foreign, individual-specific antigens, these cells usually become immunologically activated and attack the host. This phenomenon is descriptively called a graft-versus-host reaction (GVHR). The factors which influence the pathogenesis of such reactions are multiple and varied; however, experiments can be designed in which the most important variable influencing the intensity of the GVHR is antigenic disparity. For this reason, the GVHR can be utilized to evaluate the degree of histoincompatibility existing between various members of a species. At present, the clearest application of this principle is the demonstration by Brent and Medawar that the intensity of local cutaneous inflammatory lesions in a panel of prospective donor guinea pigs, following the injection of lymphoid cells from a prospective recipient, correctly predicted the order with which the latter rejected skin grafts from members of that panel.’ Unfortunately, little is known about the antigens responsible for the elicitation of GVHR’s. It is generally assumed that the histocompatibility factors recognized in the GVHR are those involved in the rejection of a foreign skin, tumor, or organ graft by the host. However, pertinent evidence on this point has been derived from only two species, the chicken and the mouse. In both species, it is known that many histocompatibility (H) loci exist, but apparently only the products of a single locus in each case are sufficiently immunogenic to elicit a GVHR when moderate doses of lymphoid cells from normal (i.e., unsensitized) donors are employed. Because of these findings, Simonsen has suggested that techniques involving the induction of GVHR’s by normal lymphocyte transfer (NLT) might be utilized to test 2-8

Transplantation Immunity of Gestational Origin in Infant Rats

Comparison of the survival times of homografts of BN skin on 3-day-old Lewis rats born of mothers of the same isogenic strain with those of BN grafts on infant Lewis hosts that had developed in an F1 (Lewis x BN) hybrid, gave no evidence of maternally induced tolerance as a result of development in an antigenically alien environment. On the contrary, the significantly shorter median survival time of the grafts on the hybrid-derived Lewis group suggests that sensitization had occurred as a consequence of natural exposure during gestation to small numbers of maternal cells.

TYPING AND IMMUNOSUPPRESSION IN RATS

Mixed leukocyte culture tests were carried out on a heterogeneous but genetically defined backcross population of rats to determine whether the reactions observed were related to histoincompatibility. The genetic situation precluded two-way reactions. Only when the two donors of a leukocyte mixture differed at the important Ag-B histocompatibility locus was there any in vitro reactivity, and a difference at this locus was always associated with an acute homograft reaction. Compatibility at this locus proved to be important in that it facilitated the prolongation of survival of skin homografts by immunosuppressive therapy.

VARIABLE EXPRESSION OF Ag-B AND NON-Ag-B HISTOCOMPATIBILITY ANTIGENS ON CULTURED RAT CELLS OF DIFFERENT HISTOLOGICAL ORIGIN

Cells cultured from different tissues and organs of various aged rats were tested by the mixed hemagglutination assay (MHA) for the presence of several histocompatibility antigens. Chronological or histological variations in expression of antigens determined by the major histocompatibility locus of the rat, Ag-B, were exhibited by cell lines derived from both embryonic and adult tissues. Ag-B antigens were detected on primary cultures of cells from neonatal brain, skin, liver, heart, eye, spleen, and kidney. A peculiarity of the kidney-derived cultures was the presence of patches of epithelial cells which did not react with any antiserum tested, including a heterologous rabbit antirat serum. Non-Ag-B antigens, including a male-associated antigen, were also detected with MHA. These antigens were present on cultured tissue cell lines, but not on any of the organ-derived cultures, except skin. The epithelial-like cells of skin cultures, but not the fibroblasts, were reactive. A collagen-mediated masking phenomenon which markedly reduced or climinated reactivity of non-Ag-B antisera was also revealed.

Further studies on the number of histocompatibility loci in rats

The response of (DA×BN.B2)F2 rats to small skin grafts from each of the inbred parental strains indicated that at least 15 histocompatibility loci were segregating. The results are discussed with respect to other F2 analyses.