HLA and Aplastic Anemia: associations In Large Brazilian Cohorts

Aplastic anemia (AA) is perceived as an immune mediated disease where T-lymphocytes recognize and destroy bone marrow elements leading to varying degrees of failure of hematopoiesis. Many autoimmune diseases have been linked to certain HLA alleles and such a relationship has been also been reported in AA. Expansion of CD8+ oligoclones has been reported in AA and likely contributes to pathogenesis. However, the interaction of CD4+ and CD8+ T cells and their targets mediated by human leukocyte antigen (HLA) class I and II peptides remain elusive. Thus, it has been speculated that polymorphic loci of these genes could be implicated in the susceptibility to the disease. Various alleles and haplotypes of HLA molecules have been implicated in the predisposition of AA development. The influence of HLA has been studied in North America, European and Asian countries. Data from Latin America, where there is a large mixture of Hispanic, European, and African descendants, is still lacking. This study focuses on the association between HLA alleles in AA patients in different regions of Brazil with particular ethnic groups.

From 2000 to 2013, all patients with a diagnosis of acquired AA in the Brazilian state of Bahia (BA) followed at the Federal University of Bahia Hospital/ Foundation Hemoba who tested the HLA typing were included, totaling 215 patients. In this northeast region there is a predominance of African descendant (25% white, 75% brown/black). The genes in the analysis included HLA A, B, DR and DQ. SPSS was used to statistical calculations. Qui-square test/Fisher test were using the p-value correction of Bonferroni (p significant <0,0016) for comparison of genetic varieties.The HLA of patients with acquired AA Bahia (n = 215) were compared to the control group (3680 healthy non-related bone marrow volunteers donors from Bahia).

To address regional differences within the country we also analyzed the HLA of AA patients (n = 344) from the State of Paraná located in the southern portion of the country and is characterized by a diverse ethnic mixture (71.3% white and 27% black/brown). Thus, we compared the findings of HLA associated with acquired AA in the two states, Bahia (northeast region) and Parana( south region). Of those statistically associated with AA (p<0,0016), we considered HLA clinically relevant only those present in at least 10% of cases and/or controls.

From the 559 AA patients analysed, 45,1% were women, and 54.9% were men.The mean age was 23.4 (± 12.3).

Among the HLA antigens with OR of risk or protection only HLA DR15 and B15, were significant, respectively (in both populations: Bahia and Parana). Identified as a risk factor for development of AA, HLA DR15 was found in 41.6% of patients (Bahia) versus 24% in controls (OR: 2.23 - CI: 1.68 to 2.9) (p <0.0001). As protective factor for AA development the HLA B15 was found in only 6% of patients (Bahia) versus 21.3% of controls (OR: 0.213, CI 0.12 to 0.370) (p <0.0001).

A stratified analysis was conducted to assess the presence of interaction between the antigens DR15 and B15 in AA patients. When analyzing synergistically, the effects of HLA DR15 and B15, we observed that, in the AA group, the positivity of DR15+ of 41,6% falls significantly to 14,8%, when concurrently with the presence of B15+. The AA risk factor of HLA DR15+ loses its statistical risk power in presence of B15+. The incidence of B15+ patients (6% in AA patients) falls to 4% in the presence of DR15 negativity (p=ns).

We observed in 2 large AA cohorts (totaling 559 patients) from very distinct ethnic regions of Brazil, that, in both, HLA DR15 positivity was associated with a higher risk of disease, while B15 positivity was associated with a lesser likelihood of developing AA.

The synergic combination of these alleles appears to be further associated with AA development. New studies analyzing synergic effect between HLA antigens/alleles should be conducted in immuno-mediated diseases.

No relevant conflicts of interest to declare.