Sarcoidosis and tuberculosis: a connection to the human leukocyte antigen system

Infectious, genetic factors, and autoimmunity have been considered as potential causes of sarcoidosis (SA). Pathological similarities between SA and tuberculosis (TB) suggest M. tuberculosis antigen(s) as causative agent(s). Our published comparative analysis of the human leukocyte antigens (HLA) system in patients with SA or TB in the same ethnic group revealed that some antigens were connected with high risk of developing of SA or TB, but other were comparable in both patient populations. Is it possible that the predominating occurrence of HLA antigens characteristic for TB may cause tuberculosis in patients with SA? To answer this question we evaluated the HLA class I and II alleles frequency by PCR amplification with sequence-specific primers in three women with histopathologically proven pulmonary SA, who developed bacteriologically confirmed TB on a corticosteroids (CS) therapy. Analysis of HLA in every case separately revealed a trend for higher occurrence of both alleles predisposing and protecting from TB than SA, in comparison with healthy individuals in our previously mentioned HLA genotyping study. Overall, the number of alleles predisposing to TB was statistically greater than the number of alleles connected with a high risk of developing SA. Also, the frequency of protecting alleles was statistically higher for TB than for SA. Therefore, SA in these patients developed at first, and the presence of additional environmental factors, e.g., age, CS might decrease an immune response and provoked TB. There is a possibility that the occurrence of HLA antigen more associated with high risk of developing TB than SA causes the development of tuberculosis in our patients with sarcoidosis.