Opposing effects of actin signaling and LFA‐1 on establishing the affinity threshold for inducing effector T‐cell responses in mice

Abstract

Mature CD8+ T cells use a narrow antigen affinity threshold to generate tissue-infiltrating cytotoxic effector T cells and induce autoimmune pathology, but the mechanisms that establish this antigen affinity threshold are poorly understood. Only antigens with affinities above the threshold induce stable contacts with APCs, polarization of a T cell, and asymmetric T-cell division. Previously published data indicate that LFA-1 inside-out signaling might be involved in establishing the antigen affinity threshold. Here, we show that subthreshold antigens weakly activate all major distal TCR signaling pathways. Lowaffinity antigens are more dependent on LFA-1 than suprathreshold antigens. Moreover, augmenting the inside-out signaling by hyperactive Rap1 does not increase responses to the subthreshold antigens. Thus, LFA-1 signaling does not contribute to the affinitybased antigen discrimination. However, we found that subthreshold antigens do not induce actin rearrangement toward an APC, mediated by Rho-family GTPases, Cdc42, and Rac. Our data suggest that Rac and Cdc42 contribute to the establishment of the antigen affinity threshold in CD8 + T cells by enhancing responses to high-affinity antigens, or by reducing the responses to low-affinity antigens.Keywords: Actin cytoskeleton r Antigen affinity threshold r LFA-1 r Rap1 r Rho-family GTPases r T-cell receptor signalingAdditional supporting information may be found in the online version of this article at the publisher's web-site IntroductionT cells mediate adaptive immune responses against invading pathogens but must tolerate cells and structures of the host to avoid autoimmunity. The self-tolerant and self-MHC-restricted repertoire of mature T cells is shaped during thymic development by negative and positive selection, respectively. Thymocytes expressing TCRs, recognizing self-peptide-MHC with an affinity Correspondence: Dr. Ondrej Stepanek e-mail: ondrej.stepanek@img.cas.cz above the antigen affinity threshold, are removed by negative selection [1][2][3][4]. CD8/CD4-Lck coupling ratios and a signaling adaptor, Themis, were shown to be critically involved in establishing the affinity threshold for negative selection [4,5]. Peripheral T cells use a narrow antigen affinity threshold to generate differentiated effector T cells and to induce autoimmune pathology, which corresponds to the antigen affinity threshold for negative selection [2,6]. The concordance between the antigen affinity thresholds for negative selection and for effector responses substantially reduces a risk of T-cell-mediated autoimmunity [1,6] OT-I T cells were injected into a RIP-OVA host iv. Mice with glucose concentration in the urine ࣙ5000 mg/dL were considered as diseased. Data shown are derived from n = 3 (OVA, Q4R7) or n = 8 (Q4H7) mice pooled from at least two independent experiments. Statistical significance was calculated using two-tailed Fisher's exact test; OVA versus Q4H7: p = 0.006, Q4R7 versus Q4H7: p = 0.006.T cells, they can trigger some level of proliferation and production of...

Altered hematopoietic system and self-tolerance in Bardet-Biedl Syndrome

“…4C). Moreover, WT and Bbs4-deficient OT-I T cells showed the same ability to induce autoimmune diabetes upon a transfer into RIP.OVA mice expressing ovalbumin under the rat insulin promoter and subsequent priming by Listeria monocytogenes expressing ovalbumin [44,52] (Fig. 4D-E).…”

“…All mice were 5-25 weeks old and had C57Bl/6J background. B1-8 [42], RIP.OVA [43], OT-I Rag2 KO/KO [44], Vav-iCre [45,46], Cd4-Cre [47] strains were described previously. Bbs4 +/GT sperm (Bbs4 tm1a(EUCOMM)Hmgu ) was obtained from KOMP (UC Davis, CA, USA) and used for in vitro fertilization.…”

“…T-cell conjugation assay was performed as previously shown [44]. Briefly, OT-I T cells from Bbs4 FL/FL Cd4-Creor Bbs4 FL/FL Cd4-Cre + (cKO) littermates were stained with CFSE cell tracker dye, and splenocytes isolated from C57Bl/6 mice were stained with DDAO cell tracker dye.…”

Strong homeostatic TCR signals induce formation of self‐tolerant virtual memory CD8 T cells

“…All mice were 5-12 weeks old and had C57Bl/6j background. RIP.OVA (Kurts et al, 1998), OT-I Rag2 À/À (Palmer et al, 2016), CD8.4, F5 Rag1 À/À (Erman et al, 2006), and Vb5 (Fink et al, 1992) strains were described previously. Mice were bred in our facilities (SPF mice: University Hospital Basel and Institute of Molecular Genetics; germ-free mice: University of Bern, Switzerland) in accordance with Cantonal and Federal laws of Switzerland and the Czech Republic.…”

Strong homeostatic TCR signals induce formation of self-tolerant virtual memory CD8 T cells

“…All mice were 5-12 weeks old and had C57Bl/6j background. RIP.OVA [28], OT-I Rag2 -/- [41], CD8.4, F5 Rag1 -/- [15], and Vβ5 [21] strains were described previously. Mice were bred in our facilities (SPF mice: University Hospital Basel and Institute of Molecular Genetics; germ-free mice: University of Bern, Switzerland) in accordance with Cantonal and Federal laws of Switzerland and the Czech Republic.…”