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Department of Microbiology and Immunology, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153
Marginal zone B (MZB) cells are the first splenic B cells to initiate Ab secretion against polysaccharide-encapsulated Ags in vivo. This swift MZB cell response can be reproduced in vitro as LPS treatment induces Ab secretion in as little as 12 h. Conversely, in vitro LPS treatment of splenic follicular B (FOB) cells results in Ab secretion after 2–3 days. The basis for these distinct response kinetics is not understood. We performed ex vivo analysis of resting and LPS-stimulated murine MZB and FOB cells and found that MZB cells express higher levels of the LPS TLR complex RP105/MD-1 and respond to much lower concentrations of LPS than do FOB cells. Furthermore, increasing doses of LPS do not accelerate the kinetics by which FOB cells transition into Ab secretion. Ultrastructural analysis of resting cells demonstrated that rough endoplasmic reticulum is more abundant in MZB cells than in FOB cells. Additionally, RT-PCR and immunoblot analyses revealed that numerous endoplasmic reticulum resident chaperones and folding enzymes are expressed at greater levels in resting MZB cells than in resting FOB cells. Although both LPS-stimulated MZB and FOB cells increase expression of these factors, MZB cells exhibit a more rapid increase that correlates with accelerated kinetics of Ab secretion and higher per cell output of secreted IgM. These data indicate that MZB cells are equipped for exquisite sensitivity to bacterial components like LPS and poised for rapid, robust Ab production, making MZB cells ideally suited as frontline defenders in humoral immunity.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 This work was supported by National Institutes of Health Grants NIH-T32 AI007508 (to K.E.G.) and GM61970 (to J.W.B.).
2 Current address: Laboratory of Protein Dynamics and Signaling, National Cancer Institute at Frederick, 1050 Boyles Street, Building 560, Room 22-103, Frederick, MD 21702
3 Address correspondence and reprint requests to Dr. Joseph W. Brewer, Department of Microbiology and Immunology, Stritch School of Medicine, Loyola University Chicago, 2160 South First Avenue, Maywood, IL 60153. E-mail address: jbrewer{at}lumc.edu
4 Abbreviations used in this paper: MZB, marginal zone B; FOB, follicular B; ER, endoplasmic reticulum; UPR, unfolded protein response; TRAP
, translocon-associated protein ; RER, rough ER.
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