B cells accumulate in the CNS during MS. What keeps them going? In this study they find the astrocyte secrtetes factors that promote B cell survival.
Take a B cell out of its environment for a few days and you have a dead B cell. In contrast T cells last for much longer.
The Canadians have got their act together and have assembled a team to examine B cell activity. They show that astrocytes secrete factors that promote B cell survival.
Touil H, Kobert A, Lebeurrier N, Rieger A, Saikali P, Lambert C, Fawaz L, Moore CS, Prat A, Gommerman J, Antel JP, Itoyama Y, Nakashima I, Bar-Or A; Canadian B Cell Team in MS.
J Neuroinflammation. 2018 Apr 19;15(1):114.
The success of clinical trials of selective B cell depletion in patients with relapsing multiple sclerosis (MS) indicates B cells are important contributors to peripheral immune responses involved in the development of new relapses. Such B cell contribution to peripheral inflammation likely involves antibody-independent mechanisms. Of growing interest is the potential that B cells, within the MS central nervous system (CNS), may also contribute to the propagation of CNS-compartmentalized inflammation in progressive (non-relapsing) disease. B cells are known to persist in the inflamed MS CNS and are more recently described as concentrated in meningeal immune-cell aggregates, adjacent to the subpial cortical injury which has been associated with progressive disease. How B cells are fostered within the MS CNS and how they may contribute locally to the propagation of CNS-compartmentalized inflammation remain to be elucidated.
We considered whether activated human astrocytes might contribute to B cell survival and function through soluble factors. B cells from healthy controls (HC) and untreated MS patients were exposed to primary human astrocytes that were either maintained under basal culture conditions (non-activated) or pre-activated with standard inflammatory signals. B cell exposure to astrocytes included direct co-culture, co-culture in transwells, or exposure to astrocyte-conditioned medium. Following the different exposures, B cell survival and expression of T cell co-stimulatory molecules were assessed by flow cytometry, as was the ability of differentially exposed B cells to induce activation of T cells.
Secreted factors from both non-activated and activated human astrocytes robustly supported human B cell survival. Soluble products of pre-activated astrocytes also induced B cell upregulation of antigen-presenting cell machinery, and these B cells, in turn, were more efficient activators of T cells. Astrocyte-soluble factors could support survival and activation of B cell subsets implicated in MS, including memory B cells from patients with both relapsing and progressive forms of disease.
Our findings point to a potential mechanism whereby activated astrocytes in the inflamed MS CNS not only promote a B cell fostering environment, but also actively support the ability of B cells to contribute to the propagation of CNS-compartmentalized inflammation, now thought to play key roles in progressive disease.
The question is what are the factors that promote this B cell activity? This study didn't report on their identity however,
They produce IL-6, Finally, astrocytes produce BAFF (B cell activating factor of the TNF family) and promote proliferation of B cells via cell-to-cell contact based on other studies.