HLA class II deficiency is a rare autosomal recessive primary immunodeficiency characterized by the absence of HLA class II molecule expression on immune cells. This defect impairs cellular and humoral immune responses, leading to increased susceptibility to severe recurrent infections. Diagnosis relies on flow cytometry, which can detect the absence of HLA-DR expression on B lymphocytes. This study aimed to evaluate variations in HLA-DR expression among patients with HLA class II deficiency at Ibn Rochd University Hospital.
A retrospective study was conducted over four years (January 2021–March 2025) to analyze HLA-DR expression in patients suspected of immunodeficiency. Data were collected from the immuno-serology laboratory. HLA-DR expression on B lymphocytes was measured using flow cytometry after incubation with specific antibodies and erythrocyte lysis. HLA class II deficiency was defined as an expression level below 5%.
Among 426 patients analyzed, 6 (1.40%) had reduced HLA-DR expression. Four patients had expression levels below 5%, consistent with HLA class II deficiency. Two patients had residual levels of 10% and 14%, suggesting a partial defect that may still impair immune function. The average patient age was 11.33 ± 13.8 years, with a male-to-female ratio of 1.94.
The two patients with residual HLA-DR expression highlight the phenotypic variability of HLA class II deficiency. Such cases have been described in the literature, with some studies that suggesting that residual expression may be associated with a distinct clinical phenotype. It is possible that these cases have a different genetic origin, as mutations in regulatory genes like CIITA, RFX5, and RFXAP. Further genetic analysis is needed to clarify the molecular mechanisms underlying partial expression. The predominance of this condition in pediatric populations underscores the importance of early diagnosis and intervention. In Maghreb contexts, pediatricians should consider this diagnosis in the presence of severe recurrent respiratory and digestive tract infections.
