Genetic determinants of cutaneous malignant melanoma in Sinclair swine.

The role of genetic factors involved in the determination of risk of cutaneous malignant melanoma (CMM) in humans remains unclear owing to genetic heterogeneity and reliance on simplistic models of inheritance. Here, we report a statistical genetic analysis of cutaneous malignant melanoma in Sinclair swine (SSCM), a unique animal model for human CMM. Using complex segregation analysis a two-locus model involving an unknown major locus and a second locus that lies within or close to the swine leukocyte antigen (SLA) complex jointly determine risk of SSCM in pedigreed animals. These loci also influence severity of affection, accounting for approximately 20% of the phenotypic variation in quantitative tumour burden.

Common swine leucocyte antigen (SLA) haplotypes in NIH and Sinclair miniature swine have similar effects on the expression of an inherited melanoma.

Mixed lymphocyte culture and serological typing of NIH and Sinclair miniature swine indicate that the two herds share a common SLA haplotype. NIH haplotype a (International Haplotype H10) appears identical to Sinclair haplotype B, which has significant effects on the penetrance of Sinclair swine cutaneous malignant melanoma (SSCM). Offspring of crosses between melanoma-bearing Sinclair swine homozygous for the B haplotype and non-melanoma NIH aa swine have tumour incidence identical to Sinclair melanoma BB x Sinclair non-melanoma BB offspring. Our results provide further support for the involvement of the swine leucocyte antigen (SLA) complex in the inheritance of SSCM, and identify a new source of non-tumour animals that have all of the genes for SSCM except those at the tumour-initiator locus.

Developing and implementing a "basic science clerkship" for first-year students.

For over 15 years, human genetics at the University of Illinois College of Medicine at Chicago (UICMC) was taught exclusively through lectures. In 1989-90 the authors revised this course for the graduating class of 1993 in order to incorporate many features found in a clerkship experience, such as oral presentations and the exploration of differential diagnoses through patient cases. In addition to lectures, the revised course consisted of small-group work in concentrated blocks of time, involving both a library research project and problem-based learning, each of which contributed to (1) significant gains in student achievement compared with data from the class of 1992 and (2) extremely favorable assessments from the students and faculty. The format of a basic science clerkship is being adopted by other departments at UICMC. The authors suggest that this format could be used by other medical schools to integrate the basic and clinical sciences.

Rabbit major histocompatibility complex. III. Multiple class II DR beta genes and restriction fragment length polymorphism of the class II alpha and beta genes.

Several class II alpha and beta chain genes of the rabbit MHC have been cloned and classified into three distinct subregions, R-DP, R-DQ and R-DR, based on their homology to the corresponding HLA-DP, -DQ and -DR genes. The organization of the rabbit MHC class II genes has now been studied in greater detail by analysing genomic DNA of an inbred III/J strain and several other RLA-D homozygous rabbits, with DNA probes derived from cloned R-DR beta genes. Eight previously cloned R-DR beta genes were shown to be allelic forms of five R-DR beta loci. Genomic blot analyses of DNA from seven rabbits homozygous for different RLA haplotypes revealed that the germline contains a total of approximately seven class II beta genes, one DQ beta, one DP beta and five DR beta. Extensive allelic polymorphism was identified by RFLP analysis using DQ and DR probes; limited RFLP was observed with DP probes. RFLP analyses allowed us to distinguish two haplotypes which had not been previously distinguished by MLR. Such RFLP analyses will be useful for identifying MHC 'compatible' rabbits for various immunobiological studies, including transplantation.

The swine leucocyte antigen (SLA) complex and Sinclair swine cutaneous malignant melanoma.

Cutaneous malignant melanoma of Sinclair swine (SSCM) is an inherited neoplasm present at birth in a majority of affected animals. We have characterized the swine leucocyte antigen (SLA) complex of the Sinclair herd at Texas A & M University using a one-way mixed lymphocyte test and found that one particular haplotype, arbitrarily identified as haplotype B, is associated with the expression of SSCM. Only a single dose of the B haplotype is required for a dominant allele at a 'tumour initiator' locus to be fully penetrant. In addition, swine homozygous for haplotype B develop more primary tumours between birth and weaning than those heterozygous for the B haplotype. Taken together, these findings indicate that tumour initiation, in utero, and expression between birth and weaning may involve different mechanisms.

Inheritance of Sinclair swine cutaneous malignant melanoma.

Genetic studies of familial human cutaneous malignant melanoma have failed to support a single mode of inheritance. To eliminate the complexities of genetic heterogeneity, we have turned to appropriate animal models to gain insights into possible genetic mechanisms that may be applicable to the human. Cutaneous malignant melanoma of Sinclair miniature swine is an inherited malignancy with many of the histopathological characteristics of human melanoma. The actual mode of inheritance of the melanoma has not been determined. Recently, we initiated experiments to characterize the swine major histocompatibility complex in melanoma- and nonmelanoma-bearing animals. These experiments led to the discovery of two loci that are involved in the expression of exophytic melanomas. The first locus lies within the swine major histocompatibility complex where one particular haplotype produces a phenotype in which the effects of a second locus are fully penetrant. The second locus segregates independently of the major histocompatibility complex. The melanoma-producing allele at this second locus is inherited in the heterozygous state and requires a somatic mutation of the normal allele to initiate tumor development.

Induction of lymphoid cell chimerism in noninbred, histocompatible rabbits. A new model for studying allotype suppression in the rabbit.

Noninbred rabbits, matched with regard to the major histocompatibility complex (RLA-A and RLA-D loci) but mismatched for Ig allotypes, served as donors (adult) and recipients (newborn) of lymphoid cells. Lasting chimerism regularly followed the transfer of 1 x 10(8)-3 x 10(8) spleen, lymph node, or bone marrow cells, as indicated by the continued production of Ig with allotypic determinants of both donor and recipient. Typically, Ig of donor allotype accounted for 25-50% of total allotypic Ig at 4 wk of age and the amount of donor Ig produced remained stable for up to 20 mo. Total allotypic Ig levels remained normal in the chimeric rabbits. "Chimeric drift" or a gradual diminution of donor products over a period of several months, occurred in some individuals. Transfer of lymphoid cells from allotype-suppressed adult donors to newborns of appropriate allotypes did not result in specific suppression of the target allotype in the recipients. Other experiments showed that lymphoid cells from suppressed donors adoptively transferred to histocompatible recipients continued to synthesize Ig of the nonsuppressed type only. The suitability of using an outbred population of histocompatible but allotype-mismatched rabbits for analyzing allotype suppression and other immunoregulatory phenomena is demonstrated by the results presented here.

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.

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 donor's spleen. Insofar as could be determined, the recipient's 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 lymphocyte and erythrocytes, accompanied by a seemingly total replacement with those of the donor.

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

Skin grafts were exchanged between siblings from 16 inbreeding lines of rabbits. Progressive inbreeding and genome fixation through 12 generations of brother X 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 geen 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 maekers for histocompatiblity loci thathave a significant effect on allograft survival time.

Histocompatibility and tooth transplantation in the rabbit.

Allogeneic orthotopic tooth transplants in the rabbit appear to stimulate transplantation immunity reactions comparable to those encountered with the transplantation of other organs. Intact untreated teeth were shown to be as quantitatively immunogenic as skin grafts between unrelated animals. Histocompatibility matching of donor and recipient and removal of pulpal tissues were demonstrated to be effective means of ameliorating the immune response to allogeneic orthotopic tooth transplants in the rabbit.