HL-A antigens: Association with disease

Molecular mimicry and clonal deletion: A fresh look

In this article, I trace the historic background of clonal deletion and molecular mimicry, two major pillars underlying our present understanding of autoimmunity and autoimmune disease. Clonal deletion originated as a critical element of the clonal selection theory of antibody formation in order to explain tolerance of self. If we did have complete clonal deletion, there would be major voids, the infamous "black holes", in our immune repertoire. For comprehensive, protective adaptive immunity, full deletion is necessarily a rare event. Molecular mimicry, the sharing of epitopes among self and non-self antigens, is extraordinary common and provides the evidence that complete deletion of self-reactive clones is rare. If molecular mimicry were not common, protective adaptive immunity could not be all-encompassing. By taking a fresh look at these two processes together we can envision their evolutionary basis and understand the need for regulatory devices to prevent molecular mimicry from progressing to autoimmune disease.

The genetics of autoimmune thyroiditis: the first decade

Most of our current understanding of the genetic predisposition to autoimmune disease can be traced to experiments performed in the decade from 1971 to 1981. Chella David was a key contributor to this research. Many of these early steps came from studies of experimental autoimmune thyroiditis. This model has been especially valuable because essentially the same disease can occur spontaneously in selected strains of animals or can be induced by deliberate immunization. From a genetic point of view, the disease has been investigated in three different species: mice, rats and chickens. The same antigen, thyroglobulin, initiates the disease in all three species. Among the main discoveries were the relationship of autoimmune disease to the major histocompatibility complex (MHC), the interplay of different subregions within the MHC in promoting or retarding development of disease, the differing roles of MHC class II and MHC I class genes in induction and effector phases, respectively, and the cumulative effect of non-MHC genes, each of which represents a small addition to overall susceptibility. Other experiments revealed that genetic differences in thyroglobulin allotypes influence susceptibility to thyroiditis. Thyroid glands differed in different strains in vulnerability to passive transfer of antibody. The first evidence of modulatory genes on the sex-related X chromosome emerged. All of these genetic findings were concurrently translated to the human disease, Hashimoto's thyroiditis, where thyroglobulin is also the initiating antigen.

Influence of the major histocompatibility complex on disease resistance and productivity

Publications in which chickens of different B haplotypes were studied for differences in disease resistance or productivity traits are reviewed. The most prominent effects on diseases are those involving tumors, but other examples involving autoimmune disease and microbial infections not resulting in neoplasia or autoimmunity are also cited. Each referenced disease paper is briefly defined with regard to: population used, B alleles present, and the most resistant B types. Studies citing B haplotype influences on productivity and reproductive fitness traits are summarized and the most desirable B genes in each referenced population are given. Plausible mechanisms of the B haplotype's influence on the traits are briefly discussed. Based on the evidence reviewed for disease resistance and productivity traits and the central role of B-complex genes in immune function, it is concluded that poultry breeders should develop B-genotype information in their base breeding populations and use those types yielding optimal performance.

Cell-mediated immunity in autoimmune thyroid disease

The initiation of an autoimmune response requires the establishment of an appropriate microenvironment. This, in turn, involves several requirements, including antigen expression on the membrane surface of the target cells, class II antigen expression on the antigen-presenting cell or target cell, a relative systemic or local increase in the helper/inducer subset of T cells, and/or a relative decrease in the suppressor subset of T cells. All of these conditions have been described in the thyroid gland. Appropriate cellular interactions result in the appearance of activated T cells and the generation of cytotoxic T cells. The pathologic alterations may be produced by the local production of antibody and subsequent formation of immune complexes, by direct lymphocyte damage, or by lymphokine production. Autoimmune thyroid disease remains, to our minds, the most instructive paradigm of the organ-specific autoimmune endocrinopathies.

Cell-mediated immunity to dietary antigens in coeliac disease

By means of the leukocyte migration inhibition test a significant depression of migration index (indicating increased immunity) was found in 10 untreated coeliac patients compared with 24 control subjects with the dietary antigens bovine serum albumin (BSA) and egg white but not with milk. The degree of immunity was similar to that obtained with gluten fraction III as antigen. Treatment with a gluten-free diet led to a decrease in immunity to egg white and BSA, but immunity to gluten fraction III was increased in the early months of treatment.

HLA BW54 and B5 in Japanese diabetics with juvenile-onset and insulin-dependency (with special reference to the family history)

The frequency of HLA BW54 and B5 in Japanese patients with JOD is increased and decreased, respectively. In JOD patients without a family history of MOD, the frequency of BW54 is significantly increased, whereas in JOD patients with a positive family history the frequency was not increased in a statistically significant manner.

Histocompatibility antigens (HLA): associations with immunopathic diseases and with responses to microbial antigens

Described is the experience from a single histocompatibility typing laboratory sampling, firstly, Australian patients with various immunopathic diseases and, secondly, subjects previously classified as "responders" or "non-responders" to various microbial antigens. The diseases considered included chronic active hepatitis (CAH) and various cirrhoses, "thyrogastric" autoimmune diseases, systemic lupus erythematosus (SLE), rheumatoid arthritis, dermatitis herpetiformis (DH) with intestinal villous atrophy, and multiple sclerosis (MS). The immune responses considered included those to flagellin, candidin, mumps, trichophyton, tuberculin and streptococcal enzymes. The HLA specificities particularly associated with disease included B8 (CAH, thyrotoxicosis SLE, DH, and miscellaneous immunopathic diseases) and B7 (thyrotoxicosis, SLE, DH, and MS). The same specificities were present in excess, although not impressively so, among responders to certain of the microbial antigens, i.e. B7 with high responders to flagellin and B8 (and A1) with responders to trichophyton.

Factors influencing small bowel changes in dermatitis herpetiformis

Factors influencing small bowel morphology in dermatitis herpetiformis (DH) were investigated by comparing patients with DH and normal small bowel biopsies to patients with DH and abnormal small bowel biopsies. The mean age of 18 patients with morphological changes in small bowel (38 years) was significantly lower (P less than 0-001) than the mean age of nine patients with normal bowel mucosa (60 years). HLA typing confirmed the high frequency of HLA-B8 in DH (64%) but HLA-B8 was unrelated to the presence or severity of small bowel lesions. Four patients had diarrhoea with progressive weight loss or abdominal cramps subsequently responsive to gluten withdrawal. In this subgroup serum levels of IgG and IgM were significantly lower than in patients with normal small bowel mucosa. Small bowel involvement appeared to be independent of the duration and severity of skin disease, and the deposition of immunoglobulin and complement (C3) in the dermal papillae of skin adjacent to skin lesions.

Histocompatibility antigens and other genetic markers in ankylosing spondylitis and inflammatory bowel diseases

Of 118 Dutch patients suffering from ankylosing spondylitis (AS) 81-4% were found to be positive for the HLA antigen B27. The B27 frequency proved to be significantly higher in patients in whom the disease had an early onset. In addition to B27, another HLA antigen may be associated with AS; the antigen Bw 16 was found to be significantly increased in B27 negative AS patients. HLA phenotype frequencies were also determined in 109 patients with idiopathic inflammatory bwel disease (IBD). In fifty-eight ulcerative colitis (UC) patients a raised incidence of A 11 was noticed. In fifty-one patients with Crohn's disease (CD) the antigen B18 showed an increased frequency. Both deviations were statistically significant. In thirty-nine patients suffering from both AS and IBD 50% proved to be B27 positive, which is significantly diffrent from B27 frequency in patients with AS alone. In the B27 negative patients with AS and IBD and increased frequency of Bw16 was also shown.

Genetic markers and cancer epidemiology

The study of potential associations between genetic markers and various cancers has a long history in cancer epidemiology. Such investigations are subject to serious problems of statistical significance and the choice of appropriate control populations. A promising future for the use of human population genetics in cancer epidemiology may be in the investigation of genetic markers (such as the HL-A complex) which code for proteins of potential immunological or physiological importance in susceptibility or resistance to cancer. The cerumen gentic marker has played a central part in a hypothesis formulated in our laboratory for the etiology of breast cancer. A second new development in this field is likely to be the investigation of genetic markers in families with high incidence of cancer. Such families permit the simultaneous study of genetic hypotheses of cancer inheritance and the association of marker genotypes with cancer through segregation and linkage analysis.

Marek's disease: effects of B histocompatibility alloalleles in resistant and susceptible chicken lines

Lines of chickens selected from a common ancestral population for either resistance or susceptibility to Marek's disease developed contrasting frequencies of particular B alloalleles. Comparison of inoculated sibs in backcross-families revealed that the B alloalleles characterizing the two lines accounted for an eightfold difference in tumor incidence. This genetic difference in tumorigenesis associated with the alloalleles of the major histocompatibility complex is probably expressed through the cell-mediated immune system.

Genetic control of immune responsiveness in man

Interest in immunogenetics originated from two streams: (a) histocompatibility in mouse and man, and (b) inheritance of specific immune responses in the guinea pig and mouse. In the mouse, there are genes associated with the major histocompatibility complex (MHC) which (i) code for antigens determining allograft responses and mixed lymphocyte reactions, (ii) control responses to certain antigens (Ir genes), and (iii) code for cell-surface antigens which elicit specific antisera (anti-Ia). In man, there is genetic control, in part X-linked, over levels of immunoglobulins and immunoglobulin classes. Evidence for MHC-linked genetic control is derived from immune responses to (i) micro-organisms, (ii) pollen antigens, (iii) food antigens, (iv) vaccines, (v) inocuous test antigens, and (vi) autoantigens. Some evidence exists for allotype-linked genetic control. Practical aspects concern influences of the MHC on susceptibility to disease, within individuals and populations.

A biological role for the major histocompatibility antigens

A central function of the major histo-compatibility (H) antigens may be to signal changes in self to the immune system. Virus-induced modification of strong transplantation antigens apparently results in recognition by thymus-derived lymphocytes (T cells), with subsequent clonal expansion and immune elimination of cells bearing non-self determinants. The extreme genetic polymorphism found in the major H antigen systems of higher vertebrates may reflect evolutionary pressure exerted by this immunological surveillance mechanism.

Relation between the major histocompatibility (B) locus and autoimmune thyroiditis in obese chickens

Obese strain chickens develop circulating autoantibodies to thyroglobulin and lymphocytic infiltration of their thyroids during aging. Two alleles, B(1) and B(4), are found with high gene frequency at the major histocompatibility (B) locus. Greater pathology and higher antibody titers are observed in B(1)B(1) and B(1)B(4) birds than in their B(4)B(4) siblings.