Marginal zone B cells acquire dendritic cell functions by trogocytosis.

Area of Science:

• Immunology
• Cell Biology

Background:

• Marginal zone (MZ) B cells are crucial for early-life immunity, producing broad-spectrum antibodies.
• Antibody production by MZ B cells can necessitate presenting pathogen antigens on major histocompatibility complex class II (MHC II) molecules to T cells.

Purpose of the Study:

• To elucidate the mechanism by which MZ B cells acquire MHC II-antigen complexes from conventional dendritic cells (cDCs).

Main Methods:

• Investigated the interaction between cDCs and MZ B cells using trogocytosis.
• Utilized complement component 3 (C3) and complement receptor 2 (CR2) as key molecular players.
• Examined the role of the ubiquitin ligase MARCH1 in regulating MHC II display on cDCs.

Main Results:

• Complement component 3 (C3) binds to murine and human MHC II molecules on cDCs.
• MZ B cells recognize C3 via complement receptor 2 (CR2) and trogocytose MHC II-C3 complexes.
• MARCH1 on cDCs limits MHC II-C3 complex display to prevent excessive trogocytosis.

Conclusions:

• C3 binding to MHC II facilitates the trogocytic transfer of MHC II-C3 complexes from cDCs to MZ B cells.
• This transfer enables MZ B cells to acquire cDC-like properties, enhancing immune surveillance and antibody production.