Lymphopenia and Severe Combined Immunodeficiency (SCID) - Think Before You Ink.

OBJECTIVES: Severe combined immunodeficiency (SCID) represents one of the most severe forms of Primary immunodeficiency (PID) disorders, characterized by T cell lymphopenia (TCL) and lack of cellular and humoral immune responses. However, not all patients with low T cell lymphocyte counts may have an abnormal T cell immunity and the observed TCL may be a temporary suppression resulting from transient lymphopenia secondary to severe infections. In such cases, it is necessary to estimate the severity of the observed TCL by assessing thymic capabilities. METHODS: In this study, patients clinically suspected of SCID were evaluated for lymphocyte subsets analysis, naïve T cells and T cell receptor excision circles (TREC). RESULTS: Patients with transient lymphopenia had detectable TREC levels and normal naïve T cells subsets. Normalization of absolute lymphocyte counts, and T cells was seen in the patients after a short duration. CONCLUSIONS: The authors highlight the importance of detailed immunological investigations in an infant with severe infections and lymphopenia before labeling the infant as SCID.