An efficient immunoassay for the B cell help function of SARS-CoV-2-specific memory CD4⁺ T cells

Area of Science:

• Immunology
• Cell Biology

Background:

• CD4+ T cells provide essential "help" to B cells, a key component of adaptive immunity.
• Quantitative measurement of T cell-dependent B cell responses is crucial for understanding immune function.

Purpose of the Study:

• To develop an improved, sensitive antigen-specific T-B coculture assay for quantitative measurement of T cell-dependent B cell responses.
• To investigate the role of monocytes in enhancing T-B cell interactions and B cell responses.

Main Methods:

• Developed improved antigen-specific T-B cocultures capable of using as few as ~90 T cells.
• Utilized Mycobacterium tuberculosis (Mtb) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) models.
• Investigated the effects of monocyte supplementation on T-B cell cocultures.

Main Results:

• Early priming and activation of CD4+ T cells are critical for productive T-B cell interactions.
• Monocytes promote B cell survivability via BAFF and SCGF/CLEC11A, but this doesn't fully explain their enhancing effect.
• Monocyte inclusion significantly improved the activation and immunological output of SARS-CoV-2-specific memory CD4+ T-B cell cocultures.

Conclusions:

• The improved T-B coculture assay offers a more sensitive method for quantifying T cell-dependent B cell responses.
• Monocytes enhance T-B cell interactions and B cell activation, particularly for memory CD4+ T cells.
• This assay can evaluate the quality of CD4+ T cell help after vaccination or infection, including for SARS-CoV-2.