Porin of Shigella dysenteriae directly promotes Toll-like receptor 2-mediated CD4+ T cell survival and effector function

Abstract

Porin of Shigella dysenteriae type 1 up-regulated Toll-like receptor (TLR)2 on CD3-stimulated CD4+ T cells but could not induce the expression of other TLRs. TLR2 in association with myeloid differentiating factor 88 (MyD88) triggered the downstream signal transduction pathway leading to activation of mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB), and degradation of IκB, the NF-κB inhibitor. TLR2 co-stimulation by porin resulted in T cell expansion by inducing both proliferation and survival of the CD4+ T cells. Extracellular signal-regulated kinase (ERK)1/2 activation inhibitor U0126 and NF-κB translocation inhibitor SN-50 significantly inhibited proliferation of T cells, highlighting a direct role of ERK and NF-κB in the process. However, cell survival involving Bcl-XL induction was found to be regulated essentially by ERK with no significant role of NF-κB. Porin-induced proliferation was supported by induction of IL-2 and CD25 that are known to play a pivotal role in T cell expansion. Apart from inducing T cell proliferation, porin triggered effector functions of the cells, evident from TLR2- and MyD88-dependent release of type 1 cytokines tumor necrosis factor (TNF) and interferon (IFN)-γ along with the induction of type 1 chemokines macrophage-inflammatory protein (MIP)-1α and MIP-1β and their receptor CCR5. The proliferation, survival and effector function of CD4+ T cells through TLR2 co-stimulation show the capability of porin to directly turn adaptive immunity into action.