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Signaling in the immune system André Veillette University of Toronto November 29, 2006. Figure 1-3. The immune system is constituted by multiple cell types with different functions. Two types of immunity :
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Signaling in the immune system André Veillette University of Toronto November 29, 2006
Figure 1-3 The immune system is constituted by multiple cell types with different functions
Two types of immunity: 1) Innate immunity (macrophages, dendritic cells, natural killer cells) – more primitive 2) Adaptive immunity (T cells, B cells) – more evolved; allows antigen specificity
Figure 1-19 B cells produce antibodies against specific antigens T cells produce cytokines or can kill in response to specific antigens
The two types of immunity are mediated by different classes of receptors, using distinct signaling mechanims
Signaling mechanisms used by immune cells: • Immunoreceptors • Cytokine receptors • Toll-like receptors (TLRs) • 4) SLAM family receptors.
Immunoreceptors • central to the activation of all immune cells • function by activating protein tyrosine • phosphorylation
ITAM: « immunoreceptor tyrosine-based activation motif » • YxxL/I-6-7-YxxL/I • ITAMs trigger protein tyrosine phosphorylation by enabling the • sequential recruitment of two classes of cytoplasmic protein • tyrosine kinases
K273 Y505 Y394 C N SH3 SH2 kinase Y317 K396 Y519/520 N C kinase SH2 SH2 Protein tyrosine kinases in immunoreceptor signaling Lck Zap-70/ Syk
N unique linker Csk-PEP SH3 CD45 kinase SH2 P C Regulation of Src family protein tyrosine kinases N unique SH3 SH2 linker P Y394 kinase Y505 C inactive Src kinase (Lck) activated Src kinase (Lck)
ITAM: « immunoreceptor tyrosine-based activation motif » • YxxL/I-6-7-YxxL/I • ITAMs trigger protein tyrosine phosphorylation by enabling the • sequential recruitment of two classes of cytoplasmic protein • tyrosine kinases
Cytokine receptors • amplify immune responses • function by inducing protein tyrosine • phosphorylation
Toll-like receptors (TLRs) • expressed on innate immune cells • such as DCs and macrophages • are triggered by pathogen-associated • molecular patterns (PAMPs) • function by activating NFkB
Conclusions (Part I): 1) Multiple cell types are involved in immunity 2) Two types of immunity exist: innate and adaptive 3) Immune cells utilize several types of specialized receptors to control cellular functions, including immunoreceptors, cytokine receptors and Toll-like receptors 4) These receptors mediate their signals through unique and interesting mechanisms.
Y Y Y Y Y Y Y Y Y Y SLAM-related receptors NTB-A (Ly108) Ly-9 CRACC CD48 CD84 SLAM measles Ligands Ly-9 V NTB-A (Ly108) 2B4 CRACC SLAM CD84 C2 V V V V V V C2 C2 C2 C2 C2 C2 Y Y Y Y : TIYxxV/Imotif Y Y Y Y Y Y Y : TVYxxV/Imotif Y Y Y Y Y Y
Expression pattern Chromosome SAP (SH2D1A) SH2 T, NK, NK-T, eo,?B,plat X 47% 0% EAT-2 (SH2D1B) SH2 NK, DC, MF, ?plat 1 Y Y 85% 73% ERT (SH2D1C) SH2 Y Y NK (mouse) 1 SLAM-related receptors associate with SAP family adaptors
Roles of SAP (and, presumably, SLAM-related receptors) in immunity • The SAP gene is mutated in 50-70% of cases of X-linked lymphoproliferative (XLP) disease, a human immunodeficiency characterized by an abnormal response to EBV infection with fatal infectious mononucleosis, as well as a high frequency of hypogammaglobulinemias and malignant lymphomas; • SAP-deficient mice exhibit abnormal CD4+ T cell help (decreased TH2 functions), decreased Ig production, defective memory B cells, reduced NK cell cytotoxicity, absent NKT cells and altered anti-viral responses.
SAP is required for SLAM-induced protein tyrosine phosphorylation
SAP is a bifunctional adaptor linking SLAM-related receptors to FynT, a Src family kinase
The FynT SH3 domain binds an arginine-based motif at the surface of the SAP SH2 domain SH2 domain 1 30 SAP(m)MDAVTVYHGKISRETGEKLLLATGLDGSYLLRDSESVPGVYCLCVLYQGYIYTYRVSQTETGSWSAE SAP(h)MDAVAVYHGKISRETGEKLLLATGLDGSYLLRDSESVPGVYCLCVLYHGYIYTYRVSQTETGSWSAE EAT-2(m)MD.LPYYHGCLTKRECEALLLKGGVDGNFLIRDSESVPGALCLCVSFKKLVYSYRIFREKHGYYRIE EAT-2(h)MD.LPYYHGRLTKQDCETLLLKEGVDGNFLLRDSESIPGVLCLCVSFKNIVYTYRIFREKHGYYRIQ 68 126 SAP(m)TAPGVHKRFFRKVKNLISAFQKPDQGIVTPLQYPVE.KSSGRGPQAPTG.RRDSDICLNAP SAP(h)TAPGVHKRYFRKIKNLISAFQKPDQGIVIPLQYPVEKKSSARSTQGTTGIREDPDVCLKAP EAT-2(m)TDAHTPRTIFPNLQELVSKYGKPGQGLVVHLSNPIMRNNLC...QRGRRMELELNVYENTDEEYVDVLP EAT-2(h)TAEGSPKQVFPSLKELISKFEKPNQGMVVHLLKPIKRTSPS...LRWRGLKLELETFVNSNSDYVDVLP A 1 B C D E tail * * * * * * * F 2 G
Crystal structure SAP SH2-FynT SH3 complex Chan et al., 2003
Creation of a sapR78A“knock-in” mouse floxed sapR78A allele * * cgggcg TGA ATG sapR78A loxP exon 1 exon 2 exon 3 exon 4 R78A SH2 domain
IL-4 400 350 300 250 IL-4 (pg.ml-1) sap+ 200 sap- sapR78A 150 100 50 0 Anti-CD3: Anti-CD28: 0.3 1 3.0 0 0.3 0 3.0 1 P+I 0 0 TH2 defect in CD4+ T cells from sapR78A mice
fyn-/- T cells exhibit TH2 and, to a lesser extent, TH1 cytokine defects in response to TCR stimulation
DC ? MHC TCR ? T-cell SAP FynT FynT IL-4 IL-13 Regulation of TH2 cytokine production by SAP-FynT pathway Which SLAM family receptors are involved?