Perturbation of B Cell Activation in SLAM-Associated Protein-Deficient Mice Is Associated with Changes in Gammaherpesvirus Latency Reservoirs

Abstract

Signaling lymphocyte activation molecule (SLAM)-associated protein (SAP)) interactions with SLAM family proteins play important roles in immune function. SAP-deficient mice have defective B cell function, including impairment of germinal center formation, production of class-switched Ig, and development of memory B cells. B cells are the major reservoir of latency for both EBV and the homologous murine gammaherpesvirus, gammaherpesvirus 68. There is a strong association between the B cell life cycle and viral latency in that the virus preferentially establishes latency in activated germinal center B cells, which provides access to memory B cells, a major reservoir of long-term latency. In the current studies, we have analyzed the establishment and maintenance of γHV68 latency in wild-type and SAP-deficient mice. The results show that, despite SAP-associated defects in germinal center and memory B cell formation, latency was established and maintained in memory B cells at comparable frequencies to wild-type mice, although the paucity of memory B cells translated into a 10-fold reduction in latent load. Furthermore, there were defects in normal latency reservoirs within the germinal center cells and IgD+“naive” B cells in SAP-deficient mice, showing a profound effect of the SAP mutation on latency reservoirs.

Expansion of Murine Gammaherpesvirus Latently Infected B Cells Requires T Follicular Help

“…As shown in figure 1A–C, there were significantly fewer H2bYFP positive B cells in SAP-deficient mice at both doses. Consistent with previously published results [35], [36], there was also a significant reduction in the frequency of viral genome positive cells during the early establishment of latency (Fig. 1D,F).…”

“…Since previous studies have shown that infection of SAP-deficient mice with MHV68 results in reduced viral load in spleens [35], [36], we infected mice with a recombinant MHV68 that expresses yellow fluorescent protein (MHV68-H2bYFP) [31] to compare the infected B cell populations in these mice with those seen in wild type mice. Mice were infected intranasally with either a low dose (1,000 pfu) or a high dose (4×10 5 pfu) of virus, and spleens were harvested at 16–18 days post-infection.…”

“…Although SAP-deficient murine CD8 T cells have been shown to be unable to recognize B cell targets [38], they are more highly activated during infection with MHV68 [35], [36], and other factors such as increased cytokine production may play a role in controlling infection. To specifically address the role of CD4 T cells in the establishment and expansion of MHV68 latency, we performed adoptive transfers of either wild type or SAP-deficient CD4 T cells into CD4 knockout mice such that only CD4 T cells would be deficient in SAP expression.…”

“…At late times post-infection, MHV68 latency is predominantly maintained in isotype switched memory B cells [34]. While infection of SAP-deficient mice with MHV68 mimics several features of SAP deficiency in humans, XLP is not fully recapitulated [18], [35], [36]. SAP-deficient mice do not develop FIM or succumb to infection, and although persistent virus production has been noted in the lungs [18], the viral load in the spleen is actually lower than that seen in wild type mice [35], [36].…”

Enhanced Response of T Cells from Murine Gammaherpesvirus 68-Infected Mice Lacking the Suppressor of T Cell Receptor Signaling Molecules Sts-1 and Sts-2

“…Deletion of another B7 family member, 4-1BB, impairs T cell effector function and leads to increased viral latency [38]. On the other hand, mice lacking the SLAM associated protein (SAP), a negative regulator of lymphocyte signaling, have increased CD8 + T cell activation in response to infection and impaired antibody production that ultimately does not alter long term control of the virus [39], [40]. The role of mutations that generate gain-of-function T cells in the absence of other off-target B cell effects in the control of MHV68 infection has not been determined.…”