HLA class I and class II antigens in sarcoidosis

Sarcoidosis is a multisystem granulomatous disorder. Its exact cause is unknown, but it is believed that an external agent may cause the characteristic immune reaction in genetically susceptible individuals. There is therefore general recognition that genetic vulnerability to sarcoidosis is one of the potential risk factors. HLA is encoded by genes in the major histocompatibility complex on chromosome 6. These surface cells are important in presentation of antigen and play a key part in the body's immune response to external antigens. Various HLA subtypes are more common in people with sarcoidosis than in those without. Variances in vulnerability, presentation, progression and prognosis have been related to different HLA phenotypes. HLA genes offer information into the factors driving sarcoidosis and prognosticating tools. However, in Africa, including South Africa (SA), there are no data on HLA types in relation to sarcoidosis.

To determine HLA class I and II associations in SA sarcoidosis patients.

Phenotype frequencies of HLA-A, B and C and DQB1 and DRB1 were calculated for 51 consecutive patients with biopsy-proven sarcoidosis attending the respiratory clinic at Charlotte Maxeke Johannesburg Academic Hospital and 63 controls, who were potential organ donors. The frequencies of the tested HLA loci were determined by direct counting. The significance of the associations between the various loci tested for and the presence or absence of sarcoidosis was estimated from 2 × 2 tables using the χ2 test.

Of the 51 patients, 70.6% were female. The mean age was 44.6 years. Analysis of HLA class I and class II phenotypes in sarcoidosis patients revealed a significant association with HLA-B15, C4, C7, C12, C15, C16, C17, DQ3, DR8 and DR11. In addition, a significant negative (protective) association with HLA A9, A28, B12, B17 and DR2 was observed.

This HLA study in SA patients suggests that genetic factors play a role in the causation of sarcoidosis. Some HLA subtypes have a significant association with sarcoidosis in SA patients, while other subtypes may be protective. The study supported the association of HLA antigens with sarcoidosis and implies that there is a genetic predisposition to sarcoidosis in the SA population.