All patients from the initial study group were typed for HLA class I and II alleles. Although we expected an association of HLA class II genes with antibody development, we also typed class I genes as internal negative control. As expected, only small differences between antibody-negative and -positive patients were found for HLA class I alleles. Median anti-IFN-β levels were lower in HLA-C∗16 carriers (p value = 0.007, FDR = 0.095) and higher in HLA-C∗2 and HLA-B∗57 (p value = 0.03, FDR ≤ 0.1) carriers, although the associations did not reach significance after adjustment for multiple testing.