Conserved Role of mTORC1 Signaling in B Cell Immunity in Teleost Fish

Abstract

Mammalian studies have demonstrated that B cell immune responses are regulated by mechanistic target of rapamycin complex 1 (mTORC1) signaling. Teleost fish represent the oldest living bony vertebrates that contain bona fide B cells. So far, whether the regulatory mechanism of mTORC1 signaling in B cells occurred in teleost fish is still unknown. In this study, we developed a fish model by using rapamycin (RAPA) treatment to inhibit mTORC1 signaling and demonstrated the role of mTORC1 signaling in teleost B cells. In support, we found inhibition of mTORC1 signaling by RAPA decreased the phagocytic capacity, proliferation, and Ig production of B cells. Critically, Flavobacterium columnare induced specific IgM binding in serum, and these titers were significantly inhibited by RAPA treatment, thus decreasing Ab-mediated agglutination of F. columnare and significantly increasing the susceptibility of fish upon F. columnare reinfection. Collectively, our findings elucidated that the mTORC1 pathway is evolutionarily conserved in regulating B cell responses, thus providing a new point for understanding the B cells functions in teleost fish.

Role of mTORC1 Signaling in Regulating the Immune Function of Granulocytes in Teleost Fish

“…However, it should be noted that previous studies have reported conflicting findings. For example, a previous study reported that short-term exposure to RAPA may inhibit mTORC1 in mouse macrophages [ 47 , 62 ] and trout B cells [ 37 ], leading to a reduction in phagocytosis. These discrepancies are likely due to differences in phagocytosis mechanisms among different phagocytes, suggesting that mTORC1 signaling may regulate phagocytosis through distinct pathways.…”

“…To gain granulocytes, we first isolated leukocytes from the head kidney as described previously [ 37 ] with modifications. Briefly, largemouth bass head kidneys were treated with DMEM (Gibco™, Gaithersburg, MD, USA) supplemented with 5% FBS (Gibco™, Amarillo, TX, USA) and mechanically disaggregated on a 100 μm nylon cell strainer (SPL life sciences, Gyeonggi-do, Republic of Korea).…”

“…Additionally, loss of mTORC3 exhibited cellular sensitivity to RAPA [ 24 ]. Although most studies on mTORC1-mediated regulation of immune function have focused on T and B cells, its role in granulocytes requires further exploration [ 34 , 35 , 36 , 37 ]. Studies in mammals have indicated that mTOR has an important role in regulating cell proliferation and migration [ 25 , 26 , 27 ], and mTORC1 signaling is involved in granulocyte activation [ 38 ], chemotaxis [ 39 ], migration [ 40 , 41 ], and recruitment [ 35 , 42 ].…”

Rationally Designed Self-Assembling Nanovaccines Elicit Robust Mucosal and Systemic Immunity against Rhabdovirus

“…The proliferation of IgZ + B cell and IgM + B cell was analyzed by flow cytometry, as previously described. 52 WT and TLR2-KO zebrafish were anesthetized with MS-222 and injected with 5 μg of 5-ethynyl-29deoxyuridine (EdU, Invitrogen). After 24 h, leukocytes from the gill and spleen were sampled, as described above.…”

“…64 The conserved role of MAPK, NF-κB, and mTORC1 signaling pathways in adaptive immunity was also confirmed in teleost fish. 52,65 B cells and Igs represent the most important components of the adaptive immune system in vertebrates. 39 Specific B cells represent the most important components of the adaptive immune system of vertebrates.…”