Dysfunctional mitochondria, disrupted levels of reactive oxygen species, and autophagy in B cells from common variable immunodeficiency patients.

Introduction: Common Variable Immunodeficiency (CVID) patients are characterized by hypogammaglobulinemia and poor response to vaccination due to deficient generation of memory and antibody-secreting B cells. B lymphocytes are essential for the development of humoral immune responses, and mitochondrial function, hreactive oxygen species (ROS) production and autophagy are crucial for determining B-cell fate. However, the role of those basic cell functions in the differentiation of human B cells remains poorly investigated.

Methods: We used flow cytometry to evaluate mitochondrial function, ROS production and autophagy processes in human naïve and memory B-cell subpopulations in unstimulated and stimulated PBMCs cultures. We aimed to determine whether any alterations in these processes could impact B-cell fate and contribute to the lack of B-cell differentiation observed in CVID patients.

Results: We described that naïve CD19CD27 and memory CD19CD27 B cells subpopulations from healthy controls differ in terms of their dependence on these processes for their homeostasis, and demonstrated that different stimuli exert a preferential cell type dependent effect. The evaluation of mitochondrial function, ROS production and autophagy in naïve and memory B cells from CVID patients disclosed subpopulation specific alterations. Dysfunctional mitochondria and autophagy were more prominent in unstimulated CVID CD19CD27 and CD19CD27 B cells than in their healthy counterparts. Although naïve CD19CD27 B cells from CVID patients had higher basal ROS levels than controls, their ROS increase after stimulation was lower, suggesting a disruption in ROS homeostasis. On the other hand, memory CD19CD27 B cells from CVID patients had both lower ROS basal levels and a diminished ROS production after stimulation with anti-B cell receptor (BCR) and IL-21.

Conclusion: The failure in ROS cell signalling could impair CVID naïve B cell activation and differentiation to memory B cells. Decreased levels of ROS in CVID memory CD19CD27 B cells, which negatively correlate with their cell death and autophagy, could be detrimental and lead to their previously demonstrated premature death. The final consequence would be the failure to generate a functional B cell compartment in CVID patients.