Biology of the human histocompatibility leukocyte antigen (HLA) system and a hypothesis regarding the generation of autoimmune diseases

Common variants in HLA-DRA gene are associated with alcohol dependence in two Caucasian samples

HLA-DRA gene polymorphisms might play an important role in alcohol dependence (AD). We examined genetic associations of 29 single-nucleotide polymorphisms (SNPs) within the HLA-DRA gene with AD using two Caucasian samples-the Collaborative Study on the Genetics of Alcoholism (COGA) sample (660 AD cases and 400 controls) and the Study of Addiction: Genetics and Environment (SAGE) sample (623 cases and 1,016 controls). Logistic regression analysis using PLINK showed that 16 SNPs were associated with AD in the COGA sample and 13 SNPs were associated with AD in the SAGE sample (p < 0.05). The best novel signal was SNP rs2239803 associated with AD in both samples (p = 0.000817 for the COGA sample and p = 0.0026 for the SAGE sample, respectively) while one flanking SNP rs4935356 also showed strong association in both samples (p = 0.00219 and 0.0026 for the COGA and SAGE samples, respectively). Furthermore, these two SNPs revealed stronger associations in meta-analysis of these two samples (p = 8.97 × 10(-6) and 2.02 × 10(-5) for rs2239803 and rs4935356, respectively). In addition, the G-A haplotype from these two SNPs revealed a significant association with AD in both the COGA and SAGE samples (p = 0.0007 and 0.0019, respectively). These findings highlight the novel associations with HLA-DRA that may play an important role in the etiology of AD.

The molecular genetics of diabetes mellitus

Diabetes mellitus is a clinically heterogeneous disorder which is characterized by hyperglycaemia due to an absolute or relative deficiency of insulin. Both genetic and non-genetic factors contribute to its development and, as such, it represents a multifactorial disorder. In addition, it may also be, in some instances, a polygenic disorder resulting from the cumulative effects of several genes with or without environmental factors. Serological and/or DNA markers for genes that confer susceptibility to the insulin-dependent form of the disorder (IDDM; type 1) have been identified in the HLA-D region of chromosome 6 and near the insulin gene on chromosome 11. Patients with non-insulin-dependent diabetes mellitus (NIDDM; type 2) make up a more heterogeneous group than those with IDDM and it is likely that in these patients similar clinical phenotypes may be produced by different genetic defects. The synthesis of either an abnormal insulin/proinsulin molecule or an abnormal insulin receptor can confer susceptibility to NIDDM. The genes encoding insulin and the insulin receptor are on chromosomes 11 and 19, respectively. In addition, studies of restriction fragment length polymorphism and disease associations suggest that two other genes may contribute to the development of NIDDM on chromosome 11, one near the insulin gene on the short arm of this chromosome and the other near the apolipoprotein A-I gene on the long arm. None of the susceptibility genes that have been identified to date causes diabetes in the absence of other genetic or non-genetic contributing factors, which is consistent with a multifactorial or polygenic origin for this disorder.

Association of celiac disease with microsatellite polymorphisms close to the tumor necrosis factor genes

Celiac disease is tightly linked to the MHC class II region on chromosome 6. We have studied two highly polymorphic microsatellite loci, TNFa and b, near the TNF genes in the class III region of the MHC, for evidence of their association to CD, as compared to a control population. Our findings show that the microsatellite allele most significantly associated with the disease is TNFb3, which is found in 86.3% of CD patients versus 24.5% of controls, with allele frequencies of 0.5392 and 0.1290, respectively (p < 0.001). The TNFa2 allele had a frequency of 0.6122 in CD patients and 0.2627 in controls (p < 0.001), with phenotype frequencies of 87.8% and 50.0%, respectively. TNFa6 and -a11 and TNFb5 have significantly reduced frequencies in CD patients. TNFb3 shows a maximal level of linkage disequilibrium with HLA-DQB1*0201 in celiac patients. However, while the DQB1*0201/TNFa2 haplotype was strongly associated with CD, DQB1*0201 was not significantly in linkage disequilibrium with TNFa2, suggesting that TNFa2 is independently associated with CD. This association could have functional significance as TNFa2 has been correlated with high TNF production.

Evidence for a retroviral trigger in Graves' disease

An apparently high frequency of Graves' disease encountered in New Orleans, Louisiana, prompted an investigation for a possible infectious agent that might be triggering the disease in genetically susceptible individuals. We studied 40 patients with Graves' disease, and compared them to the following groups of controls: age and gender matched healthy subjects; patients with multinodular goiter (non-autoimmune thyroid controls); patients with chronic lymphocytic thyroiditis (autoimmune thyroid disease controls) and additional organ or tissue specific autoimmune controls exclusive of thyroid autoimmunity, including patients with Type I diabetes and other endocrine autoimmune complex disorders. Serum antibodies against a prototypic strain of a human intracisternal A-type retroviral particle type 1 (HIAP-1) were detected by a sensitive and specific immunoblotting assay. In 87.5% (35/40) of the Graves' disease patients there was a positive reaction against several HIAP-1-associated proteins, predominantly 97 Kd and 80 Kd, with only 5 showing no reactivity to any. In contrast, 2% (2/105) of sera from normal controls showed positive reactivity. Furthermore, only 10% (1/10) of sera from multinodular goiter control patients and 10% (1/10) of Hashimoto's patients showed reactivity (p < 0.0005). Sera from 3 of 20 (15%) of Type I diabetic patients none of whom had Graves' disease, showed reactivity but there was no reactivity in 9 other patients with one or more of the endocrine autoimmune complex disorders, including Addison's disease, vitiligo, myasthenia gravis and pernicious anemia. In addition we studied two individuals with Graves' disease from each of two families residing outside Louisiana, all of whom were positive for these antibodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of IFN-gamma on kidney cell expression of MHC class II molecules, kidney cell associated molecules and their stimulatory capacity in mixed lymphocyte kidney cell culture

Mixed cell co-cultures of lymphocytes responding to kidney cells (MLKC), islets of Langerhans (MLIC) and mixed lymphocyte culture (MLC), were used to clarify mechanisms in allogeneic and autoimmune (tissue-associated) antigen presentation. Fresh kidney cortical tubular cells (KC), Madin-Darby canine kidney (MDCK), and dog kidney (6247) (DK) cell lines were used in MLKC reactions, and islets of Langerhans were used in the MLIC as putative antigen presenting cells (APC). The stimulating cells were treated with purified or recombinant dog interferon-gamma (IFN-gamma), and the detection of class II MHC molecule expression was assessed by a moneclonal antibody (mAb) (B1F6). Transcription of MHC class II mRNA and IFN-gamma mRNA was measured by semiquantitative polymerase chain reaction, and detection of a kidney cell (tissue-associated) antigen molecule was assessed by the mAb I1F6 that recognizes 72 and 150 kDa tubular cell protein(s) (KT1). The MDCK cell line constitutively expressed low levels of MHC class II molecules and KT1. The steady-state level of the MHC class II mRNA transcription was virtually unaltered by treatment with IFN-gamma (400 units) for 48 hours; however, the MHC cell surface protein expression was enhanced. The KC and DK cell lines constitutively expressed KT1, but not MHC class II molecules; these cells required a minimum of 4000 units, and a 62-hour incubation with IFN-gamma was needed to upregulate both surface MHC class II molecules and the transcription of corresponding specific mRNA. In the MLKC reaction both the MDCK and DK cell lines, as well as fresh KC cells, could serve as lymphocyte activators. This could be amplified by exogenous IFN-gamma. The removal of APC from the responding T cell population did not reduce the IFN-gamma effect. This indicates that IFN-gamma treatment allows for the expression of all of the co-stimulating factors and/or adhesion molecules necessary for these cells to serve as (surrogate) APC (direct as opposed to indirect antigen presentation). The requirements for purified IFN-gamma to increase this amplification was greater in the MLKC reactions with kidney cells than in the MLC reactions. The mAbs anti-IFN-gamma and I1F6 differed in their ability to inhibit lymphocyte proliferation depending on the different cell types involved. The I1F6 inhibited the MDCK and DK cell-driven MLKC (in the absence of exogenous IFN-gamma).(ABSTRACT TRUNCATED AT 400 WORDS)

HLA-DPB1 glutamate 69: a genetic marker of beryllium disease

Chronic beryllium disease (CBD) is a lung disorder related to beryllium exposure and is characterized by the accumulation in the lung of beryllium-specific CD4+ major histocompatibility complex (MHC) class II-restricted T lymphocytes. Evaluation of MHC class II genes in 33 CBD cases and 44 controls has shown a negative association with HLA-DPB1*0401 (P < 0.001) and a positive association with HLA-DPB1*0201 (P < 0.05) alleles, which differ at residues 36, 55 to 56, and 69 of the beta 1 chain. Among CBD cases, 97 percent expressed the HLA-DPB1*0201-associated glutamic acid (unaffected population, 30 percent; P < 0.001) at residue 69, a position involved in susceptibility to autoimmune disorders. This suggests that HLA-DP has a role in conferring susceptibility and that residue 69 of HLA-DPB1 could be used in risk assessment for CBD.

Crohn's disease monocytes are primed for accentuated release of toxic oxygen metabolites

BACKGROUND

Inflammatory bowel disease occurs in regions of the intestine characterized by a bowel content high in bacteria. Intestinal bacteria synthesize cell wall products such as lipopolysaccharide; when normal monocytes or macrophages come in contact with these products, they can be primed to release a number of inflammatory mediators. Mediators such as toxic oxygen metabolites released as part of the respiratory burst may contribute to inflammatory tissue damage. The aim of this study was to determine if monocytes from patients with Crohn's disease are primed by lipopolysaccharide for a greater respiratory burst.

METHODS

The generation of superoxide anion was measured by superoxide dismutase inhibitable reduction of ferricytochrome c.

RESULTS

Freshly isolated monocytes from active untreated Crohn's disease patients (n = 8) showed enhanced stimulated release of superoxide anion when compared with normal monocytes (n = 15; 3.80 +/- 0.12 vs. 1.02 +/- 0.06 nmol/5 min; P < 0.001). We tested the hypothesis that the monocyte priming factor in Crohn's disease serum may be lipopolysaccharide by showing that Crohn's disease serum lost its ability to prime normal monocytes after lipopolysaccharide was removed (0.25 +/- 0.25 nmol/5 min, P < 0.001).

CONCLUSIONS

These studies indicate that bacterial cell wall products may be important proinflammatory molecules involved in the initiation and/or perpetuation of Crohn's disease.

MHC class I and autoimmune diabetes

The cause of failed self tolerance, resulting in autoimmunity is unknown, although genetic linkage to genes within the MHC class II region have been well described. We present evidence that failed self tolerance in autoimmune diabetes appears to be secondary to an antigen presenting cell defect; the diabetic antigen presenting cells fail to deliver fragments of endogenous antigens to the cell surface in the groove of MHC class I. In the diabetic NOD mouse model, this correlates with a rare allele at the Tap-1 locus, a gene that controls proper MHC class I assembly by providing fragments of endogenous peptides into the endoplasmic reticulum. We propose that MHC class I presentation of self peptides may represent a normal pathway for tolerance induction and interruption of this important class I function from any cause, including the MHC class II-linked Tap-1 and Tap-2 genes, which may result in autoreactivity.

Molecular linkage of the HLA-DR, HLA-DQ, and HLA-DO genes in yeast artificial chromosomes

Eight major histocompatibility complex (MHC) class II loci and the newly defined Y3/Ring 4 locus were isolated in overlapping yeast artificial chromosome (YAC) clones defining a 420-kb segment of human chromosome 6p21.3. YAC B1D12 spanning 320 kb contained seven of these loci from HLA-DRA to HLA-DQB2. A 330-kb YAC, A148A7, spanned from the HLA-DQA1 locus through the Y3/Ring 4 locus and extended at least 130 kb centromeric of YAC B1D12. Southern blotting demonstrated that YAC B1D12 derived from the HLA-DR3 haplotype and that YAC A148A7 derived from the HLA-DR7 haplotype of the heterozygous library donor. A third 150-kb YAC, A95C5, lay within this contig and contained only the HLA-DRA locus. A fourth 300-kb YAC, A76F11, was isolated by chromosome walking from the telomeric end of YAC B1D12. Probes isolated from the ends of the YAC genomic inserts have been used to confirm overlaps between the clones. These analyses demonstrated that the centromeric end of YAC A76F11 used the same genomic EcoRI cloning site as the telomeric end of YAC A95C5. YAC B1D12 used an EcoRI site only 2.1 kb telomeric of the aforementioned EcoRI site. These data suggest that certain EcoRI sites are used preferentially during construction of the library. These YACs complete the linkage of the DR and DQ subregions of the HLA complex in cloned DNA and provide the substrate for precise analysis of this portion of the class II region.

Insulin dependent diabetes mellitus susceptibility or protection may be determined by certain HLA-DQ molecules

On the basis of our own studies and those of others, we suggest that several DQ molecules may be involved in IDDM susceptibility (Table 2). Our studies suggest that these DQ molecules may be encoded both when the DQA1 and DQB1 genes are in cis or trans position. A common denominator of several of these IDDM susceptibility molecules is that they have a non-Asp amino acid at DQ beta chain residue 57. Our studies demonstrate that this residue may be an important residue for peptide presentation to T cells.

DNA sequence analysis and restriction fragment length polymorphism (RFLP) typing of the HLA-DQw2 alleles associated with dermatitis herpetiformis

Dermatitis herpetiformis (DH) is a blistering autoimmune skin disease associated with a 95-100% incidence of the HLA class II antigen HLA-DQw2. Although the precise role of this antigen in the pathogenesis of DH is unclear, one theory proposes that patients with DH possess a molecularly unique subtype of the HLA-DQw2 antigen that causes immune abnormalities eventuating in the clinical manifestations of DH. To test this hypothesis, we performed DNA sequence analysis on the highly polymorphic HLA-DQB1 and HLA-DQA1 loci of eight patients with dermatitis herpetiformis. All DQB1 alleles sequenced were identical to the previously described HLA-DQB*0201 allele from HLA-DQw2 normal subjects. In addition, DQA1 alleles sequenced were identical to those alleles previously associated with HLA-DQw2 (DQA*0201, DQA*0501). These data document that although HLA-DQw2 appears to be a necessary element in the pathogenesis of DH, the development of DH is not dependent on the presence of a unique HLA-DQw2 antigen. HLA-DQ allelic typing by restriction fragment length polymorphism analysis of PCR-amplified HLA-DQA1 and HLA-DQB1 fragments was also performed in ten patients with DH to determine the allelic distribution among both HLA-DR3 (eight patients) and non-DR3 (two patients) DH patients. At the HLA-DQ beta chain locus, all patients possessed the DQB1*0201 allele. At the HLA-DQ alpha chain locus, all HLA-DR3 patients and one non-DR3 patient displayed a pattern consistent with the DQA1*0501 allele, whereas one non-DR3 patient displayed a pattern consistent with the DQA1*0201 allele. These data document that patients with DH do not express a unique HLA-DQw2 heterodimer, that the HLA-DQw2 molecules present in patients with DH have no DNA sequence differences from those found in normal HLA-DQw2 subjects and therefore that susceptibility to DH is not due to a unique HLA-DQw2 molecule.

Immunogenetic findings in cutaneous lupus erythematosus

The serologic features and histocompatibility antigen associations of 93 patients with cutaneous lupus erythematosus are reported. Of them, 37 had chronic cutaneous lupus erythematosus and 56 had subacute cutaneous lupus erythematosus. Subacute cutaneous lupus erythematosus with an annular pattern occurred in 32 patients; 24 had a papulosquamous morphology. Sixty percent of patients with annular subacute cutaneous lupus erythematosus had anti-Ro antibodies. The incidence of this antibody in the other two groups was lower. In addition, patients with annular skin lesions had significant antigen association with HLA-B8 (37.5%; relative risk, 4.6) and HLA-DR3 (59.4%; relative risk, 4.3). There were no significant differences among chronic cutaneous lupus erythematosus and subacute cutaneous lupus erythematosus of the papulosquamous type and the control population for any HLA loci. Thus only patients with annular skin lesions represent a homogeneous subgroup in which there is a striking concordance of anti-Ro antibodies and the HLA-B8 and HLA-DR3 phenotypes.

Increased incidence of certain TCR and HLA genes associated with myasthenia gravis in Italians

In order to study the immunogenetics of myasthenia gravis (MG), we analysed the TCR and HLA-class II genes from Italian and Californian myasthenic patients. We investigated polymorphisms of the TCR using the full length cDNA probes pGA5 and the pT10 for the alpha and beta chains, respectively. The 6.3 kb and 2.0 kb polymorphic markers, revealed by the PssI enzyme and the alpha chain probe, were shown to be significantly associated with MG. Italian MG patients were HLA typed, and allele frequencies showed a significant association of DR3 and DQw2 with MG. The relative risk calculated for DR3 was 7.4. T-cell proliferative responses to peptides of the AchR alpha chain were also studied and no associations with TCR RFLP analysis or HLA-class II typing were observed.

Analysis of HLA-DQB and HLA-DPB alleles in Graves' disease by oligonucleotide probing of enzymatically amplified DNA

We have tested the possible association of HLA-DQB and HLA-DPB alleles with Graves' thyrotoxicosis, with or without severe ophthalmopathy, by polymerase chain amplification of genomic DNA and allele-specific oligonucleotide probing. There was no significantly abnormal distribution of DQB alleles compared to 50 control subjects except for a reduced prevalence of DQw 3.1 in the Graves' patients with severe ophthalmopathy (X2 = 6.23, P less than 0.02). HLA-DPB 2.1/8 was found in only 1 of 40 of these patients compared with 15 of the controls (X2 = 11.49, P less than 0.001). Ten of 48 patients with Graves' disease but without clinically significant eye involvement were HLA-DPB 2.1/8 positive, not significantly different from controls, but significantly different from the ophthalmopathy group (X2 = 6.70, P less than 0.01). The other DPB alleles in both groups of Graves' disease patients were the same as controls. These results suggest that HLA-DPB 2.1/8 may confer a protective effect in Graves' disease with respect to ophthalmopathy.

T cell receptor phenotypes in autoimmune thyroid disease

We have examined T cell receptor expression by peripheral blood and thyroidal lymphocytes in Graves' disease and Hashimoto's thyroiditis, using monoclonal antibodies directed against three beta chain variable region families and against the gamma chain. There was no abnormal distribution of positive staining with the beta chain reagents (compared to normal peripheral blood) in either the thyroid or the blood. However, thyroidal lymphocytes contained an excess of gamma-chain-bearing T cells, compared to peripheral blood, in five of the seven patients in whom simultaneous samples were available. The gamma-chain-positive T cells were not altered in the blood lymphocyte population of untreated Graves' patients. These results suggest that the T cell response in autoimmune thyroid disease is polyclonal and that there may be a role (such as cytotoxicity) for T cells expressing the gamma delta type of T cell receptor in thyroiditis.

Regression of adjuvant-induced arthritis in rats following bone marrow transplantation

Total body irradiation followed by bone marrow transplantation was found to be an effective treatment for adjuvant arthritis induced in rats. This treatment is most effective when applied shortly after the clinical manifestation of arthritis--i.e., 4-7 weeks after administration of Mycobacterium tuberculosis. Transplantation of bone marrow at a later stage results in a limited recovery, in that the inflammatory reaction regresses but the newly formed excessive bone is not eliminated. Local irradiation of the affected joints had no effect on the disease. It could also be excluded that the recovery of arthritis following marrow transplantation is due to lack of available antigen. Transplantation of syngeneic bone marrow is as effective as that of allogeneic bone marrow from a rat strain that is not susceptible to induction of adjuvant arthritis. The beneficial effect of this treatment cannot be ascribed to the immunosuppressive effect of total body irradiation, since treatment with the highly immunosuppressive drug Cyclosporin A resulted in a regression of the joint swelling but relapse occurred shortly after discontinuation of the treatment.

RFLP analysis of HLA-DR beta and -DQ beta genes in the Korean patients with insulin-dependent diabetes mellitus

Human genomic DNA samples from 19 Korean patients and 31 controls of known serological DR antigen specificity were studied for insulin-dependent diabetes mellitus (IDDM)-associated variation in HLA-DR beta and -DQ beta restriction fragment length polymorphisms (RFLPs). Genotyping allowed for accurate assignment of HLA-DR types. For HLA-DRw6, a 12kb/DR beta/Taq I fragment was decreased in Korean IDDM (p less than 0.05). However, we could not find an increased frequency of a 12kb/DQ beta/Bam HI fragment or decreased frequency of a 3.7kb/DQ beta/Bam HI fragment in Korean IDDM. These results suggest a possible protective role of the HLA-DRw6 specificity in IDDM, irrespective of ethnic background, the absence of a specific DQ beta RFLP pattern associated with IDDM in Koreans, and the difference of the Korean population in the genetic of IDDM, compared to the Caucasoid population.

Studies on the interaction between alpha-gliadin and HLA and T cell receptor molecules in coeliac disease

Coeliac disease has a known strong linkage with the HLA complex and has also recently been linked to the T cell receptor genes but the mechanism whereby these genes confer susceptibility is not known. This study has examined two possible mechanisms: (i) direct, lectin-like binding of alpha-gliadin (the causative agent of CD) to HLA or TcR molecules and (ii) antigenic cross-reactivity between alpha-gliadin and HLA or TcR molecules. A flow cytometer was used to assess interactions between alpha-gliadin, anti-alpha-gliadin antibodies (raised in both coeliac patients and in rabbits) and EBV-transformed B cell lines from coeliac patients and HLA-matched and mismatched normal controls. The B cell lines were shown to express HLA-DP, -DQ and -DR antigens which are also found on coeliac intestinal epithelial cells. After incubating B cell lines with alpha-gliadin over a wide range of concentrations, no binding of alpha-gliadin to any of the cell lines could be detected with either of the gliadin-specific antibodies. This suggests that HLA molecules do not bind to alpha-gliadin in a lectin-like fashion. In contrast to the B cell lines, alpha-gliadin binding to peripheral blood monocytes could be demonstrated. This binding occurred equally to patient and control monocytes and was not influenced by HLA allotype. The second possibility tested was that alpha-gliadin and the disease-associated HLA molecule bear antigenic similarities. However, neither rabbit anti-gliadin serum nor purified human alpha-gliadin antibody bound directly to the B cell lines. Using peripheral blood T cells similar results were obtained; no binding of alpha-gliadin or antibodies to alpha-gliadin was found. Thus this study shows that the HLA and TcR associations with CD are not explained by the direct binding of alpha-gliadin to these molecules nor by a sharing of antigenic determinants between alpha-gliadin and these molecules.

Effects of cyclosporin on T-cell subsets in human immunodeficiency virus disease

Cyclosporin (7.5 mg/kg daily) was given to 8 AIDS patients for 17-66 days and to 25 HIV-seropositive non-AIDS patients, 15 with stage II (T4 cells/microliter greater than or equal to 300, less than 600) and 10 with stage III (T4/microliter less than 300), for 3-6 months with the hypothesis that the drug could inhibit both HIV replication and the potential autoimmune component of HIV disease. A sustained increase over 600 T4/microliter occurred in 7 patients with stage II and 1 with stage III. T8 cells significantly decreased in most patients and lymphadenopathy disappeared in 14/16. After cyclosporin withdrawal T4 and T8 cells as well as lymphadenopathy returned to pretreatment status. Cyclosporin side effects (hypertension, creatinine increase, and anemia) were moderate and reversible. These results might stimulate biological research as well as clinical trials with cyclosporin in selected groups of HIV-seropositive subjects with the aim of delaying or preventing AIDS occurrence.

Pathogenetic relevance of HLA class II expressing thyroid follicular cells in nontoxic Goiter and in Graves' disease

HLA class II expressing thyroid follicular cells are found not only in classical thyroid autoimmune diseases, such as Graves' disease, but also in presumably nonautoimmune thyroid disorders such as nontoxic goiter. In this study the immunostimulatory function of the HLA class II expressing thyroid follicular cells derived from patients with nontoxic goiter and with Graves' disease was compared by assessing their capacity to stimulate allogeneic and autologous peripheral blood mononuclear cells, as well as cultured intrathyriodal T lymphocytes. Proliferation of allogeneic peripheral blood mononuclear cells was stimulated by thyroid follicular cells from both nontoxic goiter and Graves' disease thyroids, thus demonstrating that thyroid follicular cells from both disorders are capable of presenting alloantigens. In contrast the proliferation of autologous peripheral blood mononuclear cells was more efficiently stimulated by thyroid follicular cells from Graves' disease than from nontoxic goiter. Cultured intrathyroidal T lymphocytes proliferated specifically in response to autologous HLA class II+ thyroid follicular cells in Graves' disease, but not in nontoxic goiter. The responses were dose dependent and HLA class II restricted. Thyroid autoantigen presentation by HLA class II expressing thyroid follicular cells thus only occurs in Graves' disease, suggesting that HLA class II expression on thyroid follicular cells is an essential feature, but by itself not sufficient for the induction of autoimmunity. Additional factors, the possible nature of which is discussed must also be involved.

DNA polymorphism and the study of disease associations

Recombinant DNA approaches to disease analysis may be as applicable to studies of disease association as they are to the analysis and diagnosis of single-gene defects. Population and/or family association analyses, using restriction fragment length polymorphisms around candidate genes as markers, have been employed to study conditions such as atherosclerosis and disease with an HLA-association. Progress made to date in disease-association studies using recombinant DNA methodology is reviewed, the rationale behind such studies is examined and associated problems and pitfalls discussed.

HLA-alloantigen associations in Greek patients with Sjögren's syndrome

The frequency of HLA-A, -B, and -DR alloantigens was studied in 46 patients with primary Sjögren's syndrome (pSS), 14 patients with secondary Sjögren's syndrome (sSS) and rheumatoid arthritis (RA), 26 classical RA patients without clinical or histologic evidence of Sjögren's syndrome (SS) and 172 normal controls. A statistically significant increase in the frequency of HLA-DR5 alloantigen was observed in the pSS patients, compared with the controls (P less than 0.007, corrected). No differences were detected between pSS patients with or without extraglandular manifestations, nor were any found between anti-Ro(SSA) positive and negative patients. The frequency of HLA-DR3 alloantigen (30%) was not significantly higher in our pSS population than in controls (25%), nor was that of -DR4 in the RA or the sSS patients. The results of the present study indicate that the 'SS susceptibility gene' in Greek patients is linked with the HLA-DR5 expression gene and they support the hypothesis that the fundamental pSS gene may belong to another locus.

Restriction fragment length polymorphisms and an HLA-DRw52-associated split

The restriction fragment length polymorphism technique, employing seven restriction endonucleases, and a DR-specific repeated element probe were used to study a large panel of homozygous typing cells in order to delineate haplotypic differences within the HLA-DRw52 supertype. Most of the restriction endonucleases revealed the presence of two allelic restriction fragment length polymorphisms correlating with and splitting the HLA-DRw52 supertypic specificity. One designated A, correlated with the HLA-DRw52 typing in HLA-DR5, HLA-DR3, (non-A1, B8), and some HLA-DRw6 haplotypes. The other, designated a, correlated with the HLA-DRw52 typing in HLA-DR5, HLA-DRw8, HLA-DR3 (A1, B8), and the remaining HLA-DRw6 haplotypes. The general applicability of these findings was validated in 47 HLA-typed laboratory controls.

The individuality of the immune response

The high degree of polymorphism of the genes controlling the immune system makes immune reactivity of any being very individualized. Self non self recognition, rejection of non-self is the most clear and common expression of this individuality. Moreover antigen experience, chance and even psychological conditions may further affect the immune response characteristics so contributing to enhance the individuality of the "way of reacting" and, therefore, of susceptibility to immune-mediated diseases. In this perspective man can consider himself as a true biological ego.

Regulation of hematopoiesis by T lymphocytes and natural killer cells

T lymphocytes and natural killer (NK) cells exert both stimulatory and suppressive effects that regulate growth and differentiation of hematopoietic cells. Activated T and NK cells have been demonstrated in different pathological states of bone marrow failure and are proposed to play a role in the pathogenesis of the disease. T and NK cells have also been shown to be responsible for bone marrow graft rejection in both allogeneic and syngeneic donor/recipient combinations. Lymphocytes can regulate hematopoietic cell growth by direct cellular contact or by releasing soluble factors, such as colony-stimulating factors, immune interferon, lymphotoxin, and tumor necrosis factor, active on hematopoietic precursor cells.