Studies on B Cells in the Fruit-Eating Black Flying Fox (Pteropus alecto)

Abstract

The ability of bats to act as reservoir for viruses that are highly pathogenic to humans suggests unique properties and functional characteristics of their immune system. However, the lack of bat specific reagents, in particular antibodies, has limited our knowledge of bat's immunity. Here, we report a panel of cross-reactive antibodies against MHC-II, NK1.1, CD3, CD21, CD27, and immunoglobulin (Ig), that allows flow cytometry analysis of B, T and NK cell populations in two different fruit-eating bat species namely, Pteropus alecto and E. spelaea. Results confirmed predominance of T cells in the spleen and blood of bats, as previously reported by us. However, the percentages of B cells in bone marrow and NK cells in spleen varied greatly between wild caught P. alecto bats and E. spelaea colony bats, which may reflect inherent differences of their immune system or different immune status. Other features of bat B cells were investigated. A significant increase in sIg+ B cell population was observed in the spleen and blood from LPS-injected bats but not from poly I:C-injected bats, supporting T-independent polyclonal B cell activation by LPS. Furthermore, using an in vitro calcium release assay, P. alecto B cells exhibited significant calcium release upon cross-linking of their B cell receptor. Together, this work contributes to improve our knowledge of bat adaptive immunity in particular B cells.

Novel Insights Into Immune Systems of Bats

“…Furthermore, calcium influx was observed upon crosslinking of the BCR, suggesting that bat B cells are functional. The experiments performed on P. alecto were done on wildcaught bats, which may differ in their immune status and this is evident by the variability in data observed in this study within sampled bats (120); however, Periasamy et al also evaluated captive Eonycteris spelaea bats and again found that T cells are the dominant immune cell population in the spleen and blood (121).…”

“…Very few bat-specific antibodies that identify immune cell populations exist. To overcome this obstacle, Martinez Gomez et al and Periasamy et al screened commercially available antibodies for cross-reactivity to cells isolated from blood and primary and secondary lymphoid tissues of P. alecto bats (120,121). Using monoclonal antibodies specific to mammalian transcription factors, Martinez Gomez et al found that wildcaught P. alecto bats displayed a predominance of CD8+ T cells in the spleen, whereas CD4+ T cells were the most prevalent lymphocyte in the blood, lymph nodes, and bone marrow.…”

“…To evaluate B cell responses in bats, antibodies that recognize bat Ig, MHC-II, CD21, and CD27 were identified (121). B cells were successfully identified, although it was found that unlike humans, bats have more T cells than B cells in the blood and spleens.…”

“…Most studies on bat immune-relevant cells have been carried out on cells from fruit bats. Functional characterization of bat T and B cells have been carried out by detecting cytokines that are secreted by these cells on stimulation (120,121). NK cells from P. alecto and E. spalaea have been detected by flow-cytometry (121).…”

“…Functional characterization of bat T and B cells have been carried out by detecting cytokines that are secreted by these cells on stimulation (120,121). NK cells from P. alecto and E. spalaea have been detected by flow-cytometry (121). Macrophages from P. alecto have been detected and cultured in vitro by using P. alecto-specific reagents.…”