Although the strategic production of prolactin-inducible protein (PIP) at several ports of pathogen entry into the body suggests it might play a role in host defense, no study has directly implicated it in immunity against any infectious agent. Here, we show for the first time that PIP deficiency is associated with reduced numbers of CD4 + T cells in peripheral lymphoid tissues and impaired CD4 + Th1-cell differentiation in vitro. In vivo,
CD4+ T cells from OVA-immunized, PIP-deficient mice showed significantly impaired proliferation and IFN-γ production following in vitro restimulation. Furthermore, PIPdeficient mice were highly susceptible to Leishmani major infection and failed to control lesion progression and parasite proliferation. This susceptibility was associated with impaired NO production and leishmanicidal activity of PIP KO macrophages following IFN-γ and LPS stimulation. Collectively, our findings implicate PIP as an important regulator of CD4 + Th1-cell-mediated immunity.
Keywords: IFN-γ r Leishmania r Macrophages r Protozoan r Th1 cellsAdditional supporting information may be found in the online version of this article at the publisher's web-site
IntroductionThe mouse prolactin-inducible protein (PIP), also known as the mouse submaxillary gland protein, is a 14 kDa protein present in the saliva of mice. The function of PIP is not known, but it is suspected to play a role in host defense against pathogens [1][2][3][4][5][6] because it is expressed in tissues strategically located at several Correspondence: Dr. Jude E. Uzonna e-mail: jude.uzonna@med.umanitoba.ca ports of pathogen entry, including the skin, eyes, and mouth [7]. Although a definitive evidence showing a role for PIP in host immunity is lacking, its ability to potentially bind with several important host molecules including CD4 + T-cell receptor, IgG, actin, zinc α2-glycoprotein, fibronectin, and enamel pellicle suggests it may have important biological functions [8][9][10][11][12][13]. Indeed, it has been shown that PIP is a ligand of the CD4 molecule and a potent inhibitor of * These authors contributed equally to this manuscript.C 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.eji-journal.eu Eur. J. Immunol. 2015. 45: 1082-1091 Immunity to infection 1083 T-cell apoptosis induced by sequential CD4/T-cell receptor triggering, which in part modulates the immune response during viral infection by interfering with the functions mediated by the CD4 molecule [5,6,14]. Furthermore, PIP has been reported to exhibit a mitogenic effect for both normal and malignant breast epithelial cells [15], strongly suggesting that it might play a critical role in differentiation, proliferation, and function of immune cells.Our previous studies show that PIP KO mice have enlarged submandibular lymph nodes and thymic medulla [16]. However, to date, no studies have addressed the contributions of PIP in T-cell responses to either model Ags or infectious agents. Our major aim in the present study is to investigate whether PIP has immunoregulatory function...