HLA in juvenile dermatitis herpetiformis: clinical heterogeneity correlated with DNA and serological polymorphism

Defective prevention of immune precipitation in autoimmune diseases is independent of C4A*Q0

Increased prevalence of C4 null alleles is a common feature of autoimmune diseases. We have shown previously that complement-dependent prevention of immune precipitation (PIP) is defective in patients with systemic lupus erythematosus (SLE), and correlated this defect with C4A*Q0 and low levels of the C4A isotype. To further clarify the role of C4A in the aetiology of SLE, we now extend our studies to other diseases which have been associated with C4A*Q0. The frequency of C4A*Q0 was increased in Icelandic patients with coeliac disease (0.50; P < 0.001), Grave's disease (0.30; P = 0.002) and insulin-dependent diabetes mellitus (0.23; P = 0.04) and in British patients with dermatitis herpetiformis (0.42; P = 0.002) and this was reflected in low levels of C4A. In spite of this, PIP was normal in these patients, and in marked contrast to our previous observations on connective tissue diseases, PIP measurements in these patient groups correlated more strongly with levels of C4B (r = 0.51, P = 0.0000004) than C4A. Patients with increased levels of anti-C1q antibodies had significantly lower PIP than patients without such antibodies (P < 0.01) and a negative association of PIP with anti-C1q antibodies was also reflected in an increased prevalence (P = 0.006) and levels (P = 0.006) of anti-C1q antibodies in patients with subnormal PIP, as well as a negative correlation between PIP and anti-C1q antibodies (r = - 0.25, P = 0.02). These results show that the PIP defect cannot be explained by low levels of C4A alone and suggest that measurements of anti-C1q antibodies may be useful in future studies on the molecular cause of the PIP defect in autoimmune connective tissue disease.

HLA class II region genes and susceptibility to dermatitis herpetiformis: DPB1 and TAP2 associations are secondary to those of the DQ subregion

Classical dermatitis herpetiformis (DH) is associated with similar HLA class I, II and III polymorphisms to coeliac disease (CD). The two diseases share distinctive pathological changes to the small intestinal mucosa which reverse on withdrawal of dietary gluten. In order to determine the locus primarily associated with DH, and to examine whether there is a common genetic link predisposing to the enteropathy seen in both DH and coeliac disease, HLA-DR, DQ and DP subregion associations were investigated by HLA genotyping in 23 DH patients and 64 healthy controls. We also studied polymorphisms of the TAP2 locus, which is located between the DP and DQ subregions. Genotyping was carried out by PCR of genomic DNA with allelic assignment by sequence-specific oligonucleotide (SSO) hybridization or amplification refractory mutation system (ARMS). The strongest associations in the patient group were with HLA DRB1*0301 (91% vs 22% of controls), HLA DQB1*02 (100% vs 32% of controls) and DPB1*0101 (39% and 14%). These associations are similar to those described for CD. 100% of DH patients were positive for the DQA1*0501/DQB1*02 dimer in cis or trans and, by analogy with CD, this is probably responsible for presenting gliadin peptide implicated in the disease process. Homozygosity for DQ2 was significantly increased in the CD patient group compared to the DH patient group (65% versus 39%), and so differences in dosage of HLA class II genotypes between DH and CD may be responsible for the milder gastrointestinal symptoms characteristic of DH.

Immunoglobulin and HLA-DP genes contribute to the susceptibility to juvenile dermatitis herpetiformis

HLA-DQ genes and gluten diet are the main factors involved in the pathogenesis of Dermatitis Herpetiformis (DH), as well as Coeliac Disease (CD). However other genetic factors are probably relevant, since about 10% of the patients with DH and CD lack the DQA1*0501/B1*0201 heterodimer while the majority of individuals presenting this genotype and also being exposed to gluten diets did not suffer from these diseases. To evaluate the role of other genes, 36 Northern Italian children with DH were analysed for DNA polymorphisms at HLA-DP and immunoglobulin (Ig) heavy chain loci. DPA1*0201 and DPB1*1301 frequencies were higher in patients than in controls (Pc = 0.0357 and Pc = 0.0273). With respect to immunoglobulin heavy chain restriction fragment length polymorphisms (RFLP), the 4.6 kb SacI RFLP at the switch alpha 2 gene was more frequent in patients (0.13) than in controls (0.019; Pc = 0.036). Moreover, rare alleles or duplications in the switch regions occurred more frequently in the patients than in the controls. These results support the hypothesis of a multifactorial inheritance of DH, the HLA and Ig constant heavy chain genes being some of the loci contributing to the susceptibility. In accordance with previous CD studies, these data also confirm that DP subregion is probably involved in the pathogenesis of DH.

The fate of aggregated immunoglobulin A injected in IgA nephropathy patients and healthy controls

Organ uptake of IgA-containing immunologically active material was studied in humans by intravenous (IV) injection of 131I-labeled heat-aggregated human secretory IgA (HAS-IgA) in nine patients affected by primary IgA nephropathy and 10 normal volunteers. Aggregated secretory IgA was found to be removed almost exclusively by the liver. The peak activity in liver was reached at 21.1 minutes (range, 18 to 26 minutes) in patients and 19 minutes (range, 14 to 22 minutes) in controls. The rate of increase of liver radioactivity was found to be significantly slower in patients (with a mean slope of 5.0; range, 3.4 to 7.1 v 7.6, 5.6 to 11.4; P less than 0.02). The mean liver to precordium ratio at the peak time was significantly lower in patients (mean value, 2.3; range, 1.9 to 3.1) compared with controls (mean value, 3.3; range, 2.4 to 4.0) (P less than 0.02). These data confirm the pivotal role of the liver in the removal of aggregated IgA in humans and the defective clearance capacity of this test probe in IgA nephropathy patients.