CD22 is required for formation of memory B cell precursors within germinal centers.

Craig P Chappell,Kevin E Draves,Edward A Clark,Derya Unutmaz

doi:10.1371/journal.pone.0174661

Abstract

CD22 is a BCR co-receptor that regulates B cell signaling, proliferation and survival and is required for T cell-independent Ab responses. To investigate the role of CD22 during T cell-dependent (TD) Ab responses and memory B cell formation, we analyzed Ag-specific B cell responses generated by wild-type (WT) or CD22-/- B cells following immunization with a TD Ag. CD22-/- B cells mounted normal early Ab responses yet failed to generate either memory B cells or long-lived plasma cells, whereas WT B cells formed both populations. Surprisingly, B cell expansion and germinal center (GC) differentiation were comparable between WT and CD22-/- B cells. CD22-/- B cells, however, were significantly less capable of generating a population of CXCR4hiCD38hi GC B cells, which we propose represent memory B cell precursors within GCs. These results demonstrate a novel role for CD22 during TD humoral responses evident during primary GC formation and underscore that CD22 functions not only during B cell maturation but also during responses to both TD and T cell-independent antigens.

Highlights

The B cell-associated receptor, CD22, binds to alpha 2,6-galactose-linked sialic acids that are widely expressed throughout the body
To assess if CD22-deficient B cells were capable of undergoing the steps that normally occur during responses after T cell-dependent (TD) immunization, we transferred splenocytes from WT or CD22-/- B1-8hi mice into individual WT B6 recipients, immunized them 24 h later with 4(hydroxy-3-nitrophenyl) acetyl (NP)-chicken gamma globulin (CGG) in alum and analyzed IgG1a anti-NP Ab responses over time
Using Ly5 (CD45) expression to discriminate between WT and CD22-/- B cells by flow cytometry, we found that ~90% of B220+ NPbinding B cells were derived from Ly5.1+Ly5.2+ WT B cells 125 p.i. (Fig 1D)

Summary

Introduction

The B cell-associated receptor, CD22, binds to alpha 2,6-galactose-linked sialic acids that are widely expressed throughout the body. Co-transfers and immunizations were performed as above and NP-binding B cells were analyzed by flow cytometry 7 days p.i. Both WT and CD22-/- NP-binding B cells expanded to similar frequencies (Fig 2A and 2B).

Results

Conclusion