Immunoglobulin profile and B‐cell frequencies are altered with changes in the cellular microenvironment independent of the stimulation conditions

INTRODUCTION: B‐cells are essential in the defense against Mycobacterium tuberculosis. Studies on isolated cells may not accurately reflect the responses that occur in vivo due to the presence of other cells. This study elucidated the influence of microenvironment complexity on B‐cell polarization and function in the context of tuberculosis disease. METHODS: B‐cell function was tested in whole blood, peripheral blood mononuclear cells (PBMCs), and as isolated cells. The different fractions were stimulated and the B‐cell phenotype and immunoglobulin profiles analyzed. RESULTS: The immunoglobulin profile and developmental B‐cell frequencies varied for each of the investigated sample types, while in an isolated cellular environment, secretion of immunoglobulin isotypes immunoglobulin A (IgA), IgG2, and IgG3 was hampered. The differences in the immunoglobulin profile highlight the importance of cell‐cell communication for B‐cell activation. Furthermore, a decrease in marginal zone B‐cell frequencies and an increase in T1 B‐cells was observed following cell isolation, indicating impaired B‐cell development in response to in vitro antigenic stimulation in isolation. CONCLUSION: Our results suggest that humoral B‐cell function and development was impaired likely due to a lack of costimulatory signals from other cell types. Thus, B‐cell function should ideally be studied in a PBMC or whole blood fraction.