Gillian Kingsbury

Identification and characterization of SF2000 and SF2001, two new members of the immune receptor SLAM/CD2 family.

Abstract. The SLAM family of human genes currently consists of seven related members of the immunoglobulin superfamily, membrane-associated proteins, including CD150 (SLAM), CD244 (2B4), CD84, CD229 (Ly-9), BLAME, CD48, and 19A. These genes are expressed to varying degrees in subsets of immune cells (T, B, natural killer, and myeloid cells) and may function as ligands or receptors. This set of genes, related to CD2 and CD58 on Chromosome (Chr) 1p98, are found clustered close together in the human genome on Chr 1q22. Four of these family members (CD150, CD244, CD84, CD229) contain conserved tyrosine motifs in their cytoplasmic tails that enable them to bind intracellular signaling molecules SAP and EAT-2. SAP is mutated in human X-linked lymphoproliferative disease (XLP), and studies in XLP patients have shown that improper signaling via molecules that bind SAP contributes to the disease. We have identified two new members of the SLAM family (SF), which we term SF2000 and SF2001, which are expressed in immune cells and map in the SLAM gene cluster. SF2001 does not contain SAP-binding motifs in its short cytoplasmic tail. SF2000, which is co-expressed with SAP in T cells, binds both SAP and EAT-2. The data suggest that signaling through SF2000, together with CD150, CD244, CD84, and CD229, is controlled by SAP and therefore contributes to the pathogenesis of XLP.

Cloning, Expression, and Function of BLAME, a Novel Member of the CD2 Family

The CD2 family is a growing family of Ig domain-containing cell surface proteins involved in lymphocyte activation. Here we describe the cloning and expression analysis of a novel member of this family, B lymphocyte activator macrophage expressed (BLAME). BLAME shares the structural features of the CD2 family containing an IgV and IgC2 domain and clusters with the other family members on chromosome 1q21. Quantitative PCR and Northern blot analysis show BLAME to be expressed in lymphoid tissue and, more specifically, in some populations of professional APCs, activated monocytes, and DCs. Retroviral forced expression of BLAME in hematopoietic cells of transplanted mice showed an increase in B1 cells in the peripheral blood, spleen, lymph nodes, and, most strikingly, in the peritoneal cavity. These cells do not express CD5 and are CD23lowMac1low, characteristics of the B1b subset. BLAME may therefore play a role in B lineage commitment and/or modulation of signal through the B cell receptor.

ICOS expression by activated human Th cells is enhanced by IL-12 and IL-23: increased ICOS expression enhances the effector function of both Th1 and Th2 cells.

Previous mouse studies have shown that IL-4 increases the expression of ICOS on activated Th cells, resulting in enhanced ICOS expression on Th2 cells. In this study, we show that ICOS expression on human Th cells is not increased by IL-4, but by IL-12 and by IL-23 instead. Consequently, ICOS expression during IL-12-driven Th1 cell polarization was transiently increased compared with the levels on Th0 cells and IL-4-driven Th2 cells. Addition of IL-12 and/or IL-23 during restimulation increased ICOS expression to the same extent on pre-established Th1, Th2, and Th0 cells, indicating that ICOS levels are not stably imposed by prior polarization. In contrast to the findings in the mouse, IL-4 significantly suppressed the ICOS-enhancing effects of IL-12 and IL-23. The functional consequence of variable ICOS levels was shown in coculture experiments with cells expressing the ICOS-ligand B7-related protein 1 (either transfected Chinese hamster ovary cells or autologous dendritic cells). Ligation of ICOS on 2-day-preactivated effector cells increased their cytokine production to an extent proportional to their ICOS expression levels. As the ICOS-enhancing potentials of IL-12 and IL-23 were maintained for several days after stimulation, both on Th1 and Th2 cells, we propose the concept that local regulation of ICOS expression on activated Th cells by IL-12 and/or IL-23 may provide a powerful means to amplify effector T cell responses in peripheral tissues, independently of the polarized state of the Th cells.

ICOS-mediated signaling regulates cytokine production by human T cells and provides a unique signal to selectively control the clonal expansion of Th2 helper cells.

The CD28 homologue inducible costimulator (ICOS) has been demonstrated to regulate a number of T cell‐dependent immune responses in vivo. However, the expression and functional importance of ICOS during APC‐Th cell interaction in the human is not fully understood. Here, we demonstrate that ICOS‐mediated signaling plays an important role in the production of selective cytokines during both primary and subsequent Th cell responses upon allospecific or superantigen activation. In contrast, ICOS does not play a role in the differentiation of naive cells into Th1 or Th2 effector cells, nor does it determine the type of effector function of memory cells upon subsequent allogeneic challenge. In addition, our data demonstrate that ICOS provides a novel and unique role in regulating DC‐mediated Th2, but not Th1 cell clonal expansion. These data suggest that ICOS‐mediated signaling plays a discrete role in the regulation of human T helper cell responses.

ICOS and B7 costimulatory molecule expression identifies activated cellular subsets in rheumatoid arthritis.

To better define important cell subsets expressing activation markers in rheumatoid arthritis (RA), we compared selective lymphocyte and monocyte B7H1, B7H2, B7RP.1, B7RP.2, and inducible costimulatory molecule (ICOS) expression from normal peripheral blood (NL PB), RA PB, and RA synovial fluid (SF) by multicolor flow cytometry and immunohistochemistry. RA SF memory lymphocytes expressed B7RP.1 and B7RP.2, suggesting that T‐cells may function as antigen presenting cells (APCs) in RA joints. We found similar results for ICOS expression. RA SF CD14+ monocytes also expressed B7RP.1 (an ICOS ligand) and the homologous ligand B7RP.2, identifying monocytes as potential mediators of antigen processing and lymphocyte activation in RA. Furthermore, we found an increased population of RA SF CD14+ monocytes expressing B7H1 and B7H2. [The FACS analysis was supported by immunohistochemistry, showing intense lymphocyte and APC (macrophages with dendritic morphology) ICOS staining in RA synovial tissue (ST). Overall, these results define elevated populations of memoryT‐lymphocytes expressing proinflammatory B7 molecules in RA SF that either stimulate T cells through ICOS (via ICOS ligands B7RP.1 and B7RP.2), or down‐regulate RA ST T‐lymphocytes through B7H1 and B7H2.] Therefore, in the same joint, there may exist positive and negative influences on the inflammatory response, and perhaps, the negative signals dominate as joint inflammation resolves.