Salivary glands act as mucosal inductive sitesviathe formation of ectopic germinal centers after site‐restricted MCMV infection

Abstract

We investigated the hypothesis that salivary gland inoculation stimulates formation of ectopic germinal centers (GCs), transforming the gland into a mucosal inductive site. Intraglandular infection of mice with murine cytomegalovirus (MCMV; control: UV-inactivated MCMV) induces salivary gland ectopic follicles comprising cognate interactions between CD4(+) and B220(+) lymphocytes, IgM(+) and isotype-switched IgG(+) and IgA(+) B cells, antigen presenting cells, and follicular dendritic cells. B cells coexpressed the GC markers GCT (57%) and GL7 (52%), and bound the lectin peanut agglutinin. Lymphoid follicles were characterized by a 2- to 3-fold increase in mRNA for CXCL13 (lymphoid neogenesis), syndecan-1 (plasma cells), Blimp-1 (plasma cell development/differentiation), and a 2- to 6-fold increase for activation-induced cytidine deaminase, PAX5, and the nonexcised rearranged DNA of an IgA class-switch event, supporting somatic hypermutation and class-switch recombination within the salivary follicles. Intraglandular inoculation also provided protection against a systemic MCMV challenge, as evidenced by decreased viral titers (10(5) plaque-forming units to undetectable), and restoration of normal salivary flow rates from a 6-fold decrease. Therefore, these features suggest that the salivary gland participates in oral mucosal immunity via generation of ectopic GCs, which function as ectopic mucosal inductive sites.

Viral Persistence Induces Antibody Inflation without Altering Antibody Avidity

“…In mice, replicating virus at late time points postinfection can be observed in salivary glands, but whether the viral production at this site contributes to the observed antibody inflation remains to be examined. Nevertheless, it has been observed that following intraglandular MCMV infection the salivary gland can operate as a mucosal inductive site for isotype-switched IgG ϩ B cells (46). Moreover, studies by the Reddehase laboratory showed that in other tissues, such as lungs, viral replication is abortive, as only the expression of (immediate) early genes are observed, which nonetheless can lead to stimulating inflationary T cells (47).…”

Potential of Cells and Cytokines/Chemokines to Regulate Tertiary Lymphoid Structures in Human Diseases

“…Do the specific cells or cytokines contribute much to TLS formation and maintenance? And Epstein-Barr virus is thought to be a critical factor that determines TLS formation (91), as is murine cytomegalovirus in the salivary glands (92); therefore, do viruses affect TLS formation/function? In addition, is TLS development driven by different disease subtypes, or are TLS the inevitable result of persistent inflammation?…”

Ectopic lymphoid follicles: inducible centres for generating antigen‐specific immune responses within tissues

“…and Mycobacterium tuberculosis bacteria, as well as influenza and hepatitis C viruses, have been linked with ELF development in mice and humans 77, 78, 79, 80, 81, 82, 83, 84. Interestingly, ELF formation in response to infection features at mucosal sites including lung, gastric and salivary gland tissues 78, 82, 85. ELFs that develop in response to microbiota are also important for maintaining intestinal homeostasis 86.…”

“…T cells expressing CXCR5 displayed Tfh‐ and Th1‐like effector characteristics and were important for host survival, M. tuberculosis clearance, T‐cell localization within ELFs, and lymphoid follicle formation 79. In murine cytomegalovirus infection, lymphoid follicles that form in the salivary glands participate as inductive sites in oral mucosal immunity 85. Development of these salivary follicles was accompanied by a local expression of homeostatic chemokines and molecular markers such as AID and I μ C α (the non‐excised rearranged DNA of IgA class‐switching), which regulate germinal centre activities including somatic hypermutation and class‐switch recombination 85…”