Cutting Edge: Lectin-Like Transcript-1 Is a Ligand for the Inhibitory Human NKR-P1A Receptor

This information is current as David B. Rosen, Jayaram Bettadapura, Mohammed of September 27, 2021. Alsharifi, Porunelloor A. Mathew, Hilary S. Warren and Lewis L. Lanier J Immunol 2005; 175:7796-7799; ; doi: 10.4049/jimmunol.175.12.7796

http://www.jimmunol.org/content/175/12/7796 Downloaded from

References This article cites 27 articles, 15 of which you can access for free at: http://www.jimmunol.org/content/175/12/7796.full#ref-list-1 http://www.jimmunol.org/

Why The JI? Submit online.

• Rapid Reviews! 30 days* from submission to initial decision

• No Triage! Every submission reviewed by practicing scientists

• Fast Publication! 4 weeks from acceptance to publication by guest on September 27, 2021

*average

Subscription Information about subscribing to The Journal of Immunology is online at: http://jimmunol.org/subscription Permissions Submit copyright permission requests at: http://www.aai.org/About/Publications/JI/copyright.html Email Alerts Receive free email-alerts when new articles cite this article. Sign up at: http://jimmunol.org/alerts

The Journal of Immunology is published twice each month by The American Association of Immunologists, Inc., 1451 Rockville Pike, Suite 650, Rockville, MD 20852 Copyright © 2005 by The American Association of Immunologists All rights reserved. Print ISSN: 0022-1767 Online ISSN: 1550-6606. THE

JOURNAL OF IMMUNOLOGY CUTTING EDGE

Cutting Edge: Lectin-Like Transcript-1 Is a Ligand for the Inhibitory Human NKR-P1A Receptor1 David B. Rosen,* Jayaram Bettadapura,† Mohammed Alsharifi,† Porunelloor A. Mathew,‡ Hilary S. Warren,2† and Lewis L. Lanier2,3*

Increasingly, roles are emerging for C-type lectin receptors mAb inhibits human NK cell-mediated cytotoxicity against ϩ in immune regulation. One receptor whose function has FcR target cells (4, 5). remained largely enigmatic is human NKR-P1A Recently, ligands for two mouse Klrb1 family members have (CD161), present on NK cells and subsets of T cells. In this been identified (10, 11). The activating Nkr-p1f receptor rec- study, we demonstrate that the lectin-like transcript-1 ognizes Clr-g (encoded by Clec2i) (10), and the inhibitory Nkr- (LLT1) is a physiologic ligand for NKR-P1A. LLT1-con- p1d recognizes Clr-b (encoded by Clec2d) (11). Another name Downloaded from -؉ for Clr-b is osteoclast inhibitory lectin, because it was also iden taining liposomes bind to NKR-P1A cells, and binding tified as an osteoblast-derived glycoprotein, which inhibits in is inhibited by anti-NKR-P1A mAb. Additionally, LLT1 ␨ vitro osteoclastogenesis (12, 13). Although mice have multiple activates NFAT-GFP reporter cells expressing a CD3 - Clr family , only one ortholog, CLEC2D (also named lec- NKR-P1A chimeric receptor; reciprocally, reporter cells tin-like transcript-1 (LLT1)4), exists in humans. Like mouse with a CD3␨-LLT1 chimeric receptor are stimulated by Clr-b, human LLT1 blocks osteoclast differentiation (12, 13). http://www.jimmunol.org/ NKR-P1A. Moreover, LLT1 on target cells can inhibit Mouse and human Clec2 products are type II of NK cytotoxicity via interactions with NKR-P1A. The the C-type lectin superfamily. Journal of Immunology, 2005, 176: 7796–7799. The ability of mouse Nkrp1 family receptors to recognize Clr ligands prompted the question of whether this interaction is conserved in humans. In this study, we have examined whether odents have several Klrb1 (also named Nkrp1) genes LLT1 serves as a ligand of human NKR-P1A and have de- encoding either activating or inhibitory NK receptors scribed the functional consequences of this novel receptor-li- of the C-type lectin superfamily, including Nkr-p1c, R gand interaction. by guest on September 27, 2021 the NK1.1 Ag defining mouse NK cells (1). By contrast, only a single, nonpolymorphic gene in the Nkrp1 family, KLRB1, ex- ists in humans (2). KLRB1 encodes a type II disulfide-linked Materials and Methods LLT1 liposomes homodimer, named CD161 or NKR-P1A, which is expressed on most NK cells. Human NKR-P1A is on a subset of periph- A cDNA encoding the extracellular domain of LLT1 with a N-terminal 6-His ϩ ϩ tag was cloned into a pFASTBac vector, modified to encode a signal sequence eral T cells, including CD4 and CD8 T cells (mostly effec- ϩ for ecdysteroid UDP glucosyltransferase, and expressed in the Bac-to-Bac sys- tor/memory phenotype), invariant NKT cells, and ␥␦-TCR T tem (Invitrogen). Recombinant was purified by Ni-NTA affinity chro- ϩ cells, and on a subset of CD3 thymocytes (2). matography. The preparation of LLT1-fluorescent liposome complexes and the procedure for binding to cells was described previously (14–16). To ensure NKR-P1A is expressed on immature human NK cells, before binding was specific, cells were incubated with an anti-CD161 mAb or an iso- acquisition of CD16 or CD56 (3), and its expression is up-reg- type-matched control Ig (10 ␮g/ml) before incubating with the liposome- ϩ ulated on mature NK cells by IL-12 (4, 5). NKR-P1A on CD4 rLLT1 complexes. ϩ T cells and ␥␦-TCR T cells has been implicated in transen- Reporter cell assays dothelial migration (6, 7). Additionally, anti-NKR-P1A mAbs costimulate the anti-CD3 mAb-induced proliferation of An NFAT-GFP reporter construct was stably transduced into 2B4 T cell hy- bridoma cells (provided by H. Arase, Osaka University, Osaka, Japan). NFAT- CD1d-specific NK T cells (8) and induce proliferation of im- GFP reporter cells were transduced with CD3␨-LLT1 or CD3␨-NKR-P1A chi- mature thymocytes (9). Cross-linking with an anti-NKR-P1A meric receptors and analyzed as described (17, 18). Briefly, reporter and

*Department of Microbiology and Immunology, The Cancer Research Institute, and Bio- Fellow of the National Health and Medical Research Council of Australia, and a Visiting medical Sciences Graduate Program, University of California, San Francisco, CA 94143; Fellow of the Australian National University Medical School and The Canberra Hospital. †Division of Immunology and Genetics, The John Curtin School of Medical Research, L.L.L. is an American Cancer Society Research Professor. D.B.R. is supported by a The Australian National University, Canberra City, Australian Capital Territory, Austra- Genentech Graduate Student Fellowship. lia; and ‡Department of Molecular Biology and Immunology and Institute for Cancer 2 H.S.W. and L.L.L. contributed equally to this work. Research, University of North Texas Health Science Center, Fort Worth, TX 76107 3 Address correspondence and reprint requests to Dr. Lewis L. Lanier, Department of Mi- Received for publication September 27, 2005. Accepted for publication October 28, 2005. crobiology and Immunology, University of California San Francisco, 513 Parnassus Ave- The costs of publication of this article were defrayed in part by the payment of page charges. nue, Box 0414, San Francisco, CA 94143-0414. E-mail address: [email protected] This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. 4 Abbreviations used in this paper: LLT1, lectin-like transcript-1; MICA, MHC class I Section 1734 solely to indicate this fact. chain-related A. 1 This work was supported by National Institutes of Health Grant AI068129 and National Health and Medical Research Council Project Grant 151304. H.S.W. is a Senior Research

Copyright © 2005 by The American Association of Immunologists, Inc. 0022-1767/05/$02.00 The Journal of Immunology 7797 stimulator cells were cocultured at a 1:4 ratio for 16 h and then analyzed for GFP expression by flow cytometry. Constructs and transductions cDNAs for human NKp80 (provided by J. P. Houchins, R&D Systems, Min- neapolis, MN), human CD69, LLT1 with a C-terminal Flag-epitope, human NKR-P1A, and the reporter constructs were subcloned into pMXs-puro vectors (provided by T. Kitamura, University of Tokyo, Tokyo, Japan) (19). Chimeric receptors were generated by fusing the extracellular and transmembrane do- mains of either LLT1 or NKR-P1A to the intracellular domain of human CD3␨. Plasmid constructs were transfected into Phoenix packaging cells (20) to produce retroviruses (18, 21). Infected cells were selected in medium contain- ing 1 ␮g/ml puromycin. Antibodies Mouse anti-human NKR-P1A mAbs DX1 and DX12 were produced in our laboratory, and HP3G10 was purchased from MBL International. Primary cell cultures and cytotoxicity assays Venous blood was obtained from healthy volunteers, under procedures ap-

proved by the Human Ethics Committees of the Australian Capital Territory Downloaded from Department of Health and Community Care and the Australian National Uni- versity (Canberra, Australia) and the University of California, San Francisco, Committee on Human Research. Polyclonal NK cells were generated and tested in cytotoxicity assays as described previously (22–24). Results and Discussion

LLT1 liposomes bind human NKR-P1A http://www.jimmunol.org/ We generated fluorescent-labeled liposomes containing human LLT1 and evaluated their staining of the mouse Ba/F3 pro-B cell line and BaF/3 cells stably transduced with human NKR- ϩ FIGURE 1. Binding of LLT1 liposomes to NKR-P1A cells. A, Left, P1A (BaF/3-NKR-P1A). LLT1-liposome complexes bound Amounts of NKR-P1A on untransfected BaF/3 and NKR-P1A-transfected specifically to BaF/3-NKR-P1A, but not parental BaF/3 (Fig. BaF/3 cells (solid, anti-NKR-P1A; shaded, control). Right, LLT1 liposomes 1A). This interaction was specifically blocked by anti- stain BaF/3-NKR-P1A in the presence of isotype-matched control mAb (solid NKR-P1A mAb (dashed line), but not control Ig (solid). LLT1- line), but not in the presence of anti-NKR-P1A (dashed) (10 ␮g/ml), and do liposomes also bound to the human NK cell line YT transfected not stain untransfected BaF/3. B, Left, Amounts of NKR-P1A on untransfected by guest on September 27, 2021 with NKR-P1A (YT-NKR-P1A), but not to untransfected YT YT and NKR-P1A-transfected YT cells (solid line, anti-NKR-P1A; shaded, iso- cells (Fig. 1B), and the interaction was prevented by all anti- type-matched control Ig). Right, LLT1 liposomes (solid) stained YT-NKR-P1A but not YT (shaded, unstained cells). Bottom, LLT1 liposome binding to YT- NKR-P1A mAbs tested (i.e., DX1, DX12, HP3G10), but not NKR-P1A (solid line) in the presence of control Ig or blocking anti-NKR-P1A by control Ig (Fig. 1B). Furthermore, LLT1-liposomes recog- mAbs (dashed). C, Left, NKR-P1A staining of in vitro-cultured peripheral nized endogenous NKR-P1A expressed by in vitro-activated blood NK cells (solid, anti-NKR-P1A; shaded, isotype-matched control Ig). human peripheral blood NK cells, and the binding was inhib- Right, LLT1 liposome binding to in vitro-cultured NK cells alone (solid) or in ited by anti-NKR-P1A mAbs, but not by control Ig (Fig. 1C). the presence of control Ig or blocking anti-NKR-P1A mAbs (dashed). LLT1 reporter cells recognize NKR-P1A We created mouse 2B4 NFAT-GFP reporter cells (18) express- ing a chimeric protein consisting of the extracellular and trans- LLT1 inhibits NK cytotoxicity via NKR-P1A membrane domains of LLT1 and the intracellular domain of Prior studies have shown that anti-NKR-P1A mAb inhibits NK CD3␨. Receptor engagement of the CD3␨-LLT1 chimera re- cell-mediated lysis of FcR-bearing cells (2). Now with a defined sulted in signaling from the CD3␨ ITAMs, activation of ligand for NKR-P1A, we examined the function of NKR-P1A NFAT, and the expression of GFP. Coculture of the LLT1 re- in NK cells using target cells expressing its physiological ligand. porter cells with BaF/3-NKR-P1A cells resulted in robust EBV-transformed 721.221 B lymphoblastoid cells express NFAT-GFP activation, whereas coculture with parent BaF/3 or LLT1 mRNA, as detected by PCR (not shown). In accordance, BaF/3-NKp80 cells did not (Fig. 2A). Moreover, the activation we found that 721.221 activated CD3␨-NKR-P1〈 reporter of CD3␨-LLT1 reporter cells by BaF/3-NKR-P1A was specifi- cells, an effect that was blocked by anti-NKR-P1A, but not con- cally blocked by anti-NKR-P1A mAb, but not by control Ig trol Ig (Fig. 3A). (Fig. 2B). We tested the cytolytic ability of YT and YT-NKR-P1A Similarly, we created reporter cells expressing a CD3␨-NKR- against 721.221 targets. YT-NKR-P1A cells had diminished P1A chimera and tested the ability of these cells to recognize cytotoxic capacity against 721.221 compared with untrans- LLT1-bearing cells. NKR-P1A reporter cells expressed GFP fected YT (Fig. 3B); equivalent killing by YT and YT-NKR- when cocultured with LLT1-transduced BaF/3 (BaF/3-LLT1), P1A was seen against CD48-transduced BaF/3 targets, indicat- but not with untransfected BaF/3 or BaF/3 expressing human ing that both YT and YT-NKR-P1A have similar lytic potential CD69 (BaF/3-CD69) (Fig. 2C). LLT1-induced activation of (not shown). Furthermore, the NKR-P1A-mediated inhibition the NKR-P1A reporter cells was inhibited by anti-NKR-P1A of 721.221 lysis by YT-NKR-P1A cells was reversed by anti- Ј Ј mAbs, but not control Ig (Fig. 2D). NKR-P1A F(ab )2, but not control F(ab )2 (Fig. 3C). 7798 CUTTING EDGE: LLT1 IS A LIGAND OF HUMAN NKR-P1A Downloaded from http://www.jimmunol.org/

FIGURE 2. LLT1 and NKR-P1A reporter cells recognize NKR-P1A and LLT1, respectively. A, NKR-P1A-transfected BaF/3, but not parent BaF/3 or

BaF/3 expressing human NKp80, induced NFAT (as read out by GFP) when by guest on September 27, 2021 cocultured with the CD3␨-LLT1 chimera NFAT-GFP reporter cells. B, Acti- vation of CD3␨-LLT1 chimera reporter cells by BaF/3-NKR-P1A was blocked by anti-NKR-P1A. C, BaF/3-LLT1, but not parental BaF/3 or BaF/3 express- ing human CD69, induced NFAT when cocultured with CD3␨-NKR-P1A chimera NFAT-GFP reporter cells. D, Activation of CD3␨-NKR-P1A chimera reporter cells by BaF/3-LLT1 was blocked by anti-NKR-P1A (10 ␮g/ml). Max- imal stimulation in these reporter cell assays, even by cross-linking the chimeric receptor with mAb, typically results at most in ϳ60% GFPϩ cells (18).

NK cells can be stimulated through several activating recep- tors that use biochemically distinct signaling pathways, for ex- ample, human NKG2D, which recognizes MHC class I chain- related A (MICA), and human CD244, which recognizes CD48 (25). We examined the effects of NKR-P1A on these activation pathways by transducing LLT1 into BaF/3 target FIGURE 3. LLT1 inhibits NK cell-mediated cytotoxicity via NKR-P1A. A, cells expressing MICA or CD48 and determining the effect of 721.221 cells activated NKR-P1A-CD3␨ chimera reporter cells, which was NKR-P1A engagement on NK cell-mediated cytotoxicity. blocked by anti-NKR-P1A. B, YT-NKR-P1A cells have diminished cytotoxic LLT1 expression by these targets diminished NK cell-mediated capacity against 721.221 targets compared with untransfected YT cells. C, cytotoxicity induced by either the CD48/CD244 pathway (Fig. NKR-P1A-mediated inhibition of 721.221 lysis was reversed by anti- Ј Ј ␮ 3D, left) or the MICA/NKG2D pathway (Fig. 3D, right), an NKR-P1A F(ab )2, but not isotype-matched control F(ab )2 (10 g/ml). D,In vitro-cultured peripheral blood NK cell-mediated cytotoxicity against BaF/3- effect which was mediated through interactions with NKR-P1A Ј CD48 was reduced by LLT1 expression (left). LLT1-induced inhibition of NK and was reversed by anti-NKR-P1A F(ab )2, but not control cell-mediated cytotoxicity against Ba/F3-MICA was reversed by anti- Ј Ј Ј F(ab )2 (Fig. 3D). NKR-P1A F(ab )2 but not isotype-matched control F(ab )2 (right). These data prove that LLT1 is the ligand for human NKR- P1A, and this interaction inhibits NK cytotoxicity. In mice, the LLT1 ortholog Clr-b, like MHC class I, is widely expressed B-NK and B-lec interact, and whether NKR-P1A-LLT1-like (11). Recently, potential orthologs for NKR-P1A and LLT1, interactions have been preserved through evolution. LLT1 is B-NK and B-lec, respectively, have been described in the transcribed in T cells, B cells, and NK cells (27) and in osteo- chicken MHC region (26). This raises the questions of whether blast cell lines (13). The Journal of Immunology 7799

Collectively, our findings provide another example of a func- 10. Iizuka, K., O. V. Naidenko, B. F. Plougastel, D. H. Fremont, and W. M. Yokoyama. 2003. Genetically linked C-type lectin-related ligands for the NKRP1 family of nat- tional interaction between two genomically linked C-type lec- ural killer cell receptors. Nat. Immunol. 4: 801–807. tin proteins encoded by genes in the “NK complex.” This raises 11. Carlyle, J. R., A. M. Jamieson, S. Gasser, C. S. Clingan, H. Arase, and D. H. Raulet. the question of whether other C-type lectins within this 2004. Missing self-recognition of Ocil/Clr-b by inhibitory NKR-P1 natural killer cell receptors. Proc. Natl. Acad. Sci. USA 101: 3527–3532. genomic region are interacting, and what the functional conse- 12. Zhou, H., V. Kartsogiannis, Y. S. Hu, J. Elliott, J. M. Quinn, W. J. McKinstry, quences may be. Additionally, the existence of the LLT1-NKR- M. T. Gillespie, and K. W. Ng. 2001. A novel osteoblast-derived C-type lectin that inhibits osteoclast formation. J. Biol. Chem. 276: 14916–14923. P1A interaction in humans provides yet-another mechanism 13. Hu, Y. S., H. Zhou, D. Myers, J. M. Quinn, G. J. Atkins, C. Ly, C. Gange, for the fine-tuning of NK cell and T cell responses using an V. Kartsogiannis, J. Elliott, P. Kostakis, et al. 2004. Isolation of a human homolog of inhibitory receptor that recognizes a non-MHC ligand. osteoclast inhibitory lectin that inhibits the formation and function of osteoclasts. J. Bone Miner. Res. 19: 89–99. 14. Warren, H. S., A. L. Jones, C. Freeman, J. Bettadapura, and C. R. Parish. 2005. Ev- Acknowledgments idence that the cellular ligand for the human NK cell activation receptor NKp30 is not We thank Joseph Altin for providing liposomes, Mark Hulett for advice on the a heparan sulfate glycosaminoglycan. J. Immunol. 175: 207–212. Bac-to-Bac system, and Margaret Hilton, Taian Chen, and Allen Sun for tech- 15. van Broekhoven, C. L., C. R. Parish, C. Demangel, W. J. Britton, and J. G. Altin. 2004. Targeting dendritic cells with antigen-containing liposomes: a highly effective nical assistance. procedure for induction of antitumor immunity and for tumor immunotherapy. Can- cer Res. 64: 4357–4365. Disclosures 16. Van Broekhoven, C. L., and J. G. Altin. 2001. A novel system for convenient detection The authors have no financial conflict of interest. of low-affinity receptor-ligand interactions: chelator-lipid liposomes engrafted with recombinant CD4 bind to cells expressing MHC class II. Immunol. Cell Biol. 79: 274–284. References 17. Arase, H., E. S. Mocarski, A. E. Campbell, A. B. Hill, and L. L. Lanier. 2002. Direct Downloaded from 1. Plougastel, B., C. Dubbelde, and W. M. Yokoyama. 2001. Cloning of Clr, a new recognition of cytomegalovirus by activating and inhibitory NK cell receptors. Science family of lectin-like genes localized between mouse Nkrp1a and Cd69. Immunogenet- 296: 1323–1326. ics 53: 209–214. 18. Voehringer, D., D. B. Rosen, L. L. Lanier, and R. M. Locksley. 2004. CD200 receptor 2. Lanier, L. L., C. Chang, and J. H. Phillips. 1994. Human NKR-P1A: a disulfide family members represent novel DAP12-associated activating receptors on basophils linked homodimer of the C-type lectin superfamily expressed by a subset of NK and T and mast cells. J. Biol. Chem. 279: 54117–54123. lymphocytes. J. Immunol. 153: 2417–2428. 19. Kitamura, T., Y. Koshino, F. Shibata, T. Oki, H. Nakajima, T. Nosaka, and 3. Bennett, I. M., O. Zatsepina, L. Zamai, L. Azzoni, T. Mikheeva, and B. Perussia. H. Kumagai. 2003. Retrovirus-mediated gene transfer and expression cloning: pow- ϩ Ϫ Ϫ 1996. Definition of a natural killer NKR-P1A /CD56 /CD16 functionally imma- erful tools in functional genomics. Exp. Hematol. 31: 1007–1014. http://www.jimmunol.org/ ture human NK cell subset that differentiates in vitro in the presence of interleukin 12. 20. Kinsella, T. M., and G. P. Nolan. 1996. Episomal vectors rapidly and stably produce J. Exp. Med. 184: 1845–1856. high-titer recombinant retrovirus. Hum. Gene Ther. 7: 1405–1413. 4. Azzoni, L., O. Zatsepina, B. Abebe, I. M. Bennett, P. Kanakaraj, and B. Perussia. 21. Rosen, D. B., M. Araki, J. A. Hamerman, T. Chen, T. Yamamura, and L. L. Lanier. 1998. Differential transcriptional regulation of CD161 and a novel gene, 197/15a, by 2004. A structural basis for the association of DAP12 with mouse, but not human, IL-2, IL-15, and IL-12 in NK and T cells. J. Immunol. 161: 3493–3500. NKG2D. J. Immunol. 173: 2470–2478. 5. Poggi, A., P. Costa, E. Tomasello, and L. Moretta. 1998. IL-12-induced up-regulation 22. Lanier, L. L., J. J. Ruitenberg, and J. H. Phillips. 1988. Functional and biochemical of NKRP1A expression in human NK cells and consequent NKRP1A-mediated analysis of CD16 antigen on natural killer cells and granulocytes. J. Immunol. 141: down-regulation of NK cell activation. Eur. J. Immunol. 28: 1611–1616. 3478–3485. 6. Poggi, A., P. Costa, M. R. Zocchi, and L. Moretta. 1997. NKRP1A molecule is in- ϩ 23. Warren, H. S., and P. M. Rana. 2003. An economical adaptation of the RosetteSep volved in transendothelial migration of CD4 human T lymphocytes. Immunol. Lett. procedure for NK cell enrichment from whole blood, and its use with liquid nitrogen 57: 121–123. stored peripheral blood mononuclear cells. J. Immunol. Methods 280: 135–138. 7. Poggi, A., M. R. Zocchi, P. Costa, E. Ferrero, G. Borsellino, R. Placido, S. Galgani, by guest on September 27, 2021 M. Salvetti, C. Gasperini, G. Ristori, et al. 1999. IL-12-mediated NKRP1A up-reg- 24. Imai, C., S. Iwamoto, and D. Campana. 2005. Genetic modification of primary nat- ulation and consequent enhancement of endothelial transmigration of V␦2ϩ TCR ural killer cells overcomes inhibitory signals and induces specific killing of leukemic ␥␦ϩ T lymphocytes from healthy donors and multiple sclerosis patients. J. Immunol. cells. Blood 106: 376–383. 162: 4349–4354. 25. Lanier, L. L. 2005. NK cell recognition. Annu. Rev. Immunol. 23: 225–274. 8. Exley, M., S. Porcelli, M. Furman, J. Garcia, and S. Balk. 1998. CD161 (NKR-P1A) 26. Rogers, S. L., T. W. Gobel, B. C. Viertlboeck, S. Milne, S. Beck, and J. Kaufman. costimulation of CD1d-dependent activation of human T cells expressing invariant 2005. Characterization of the chicken C-type lectin-like receptors B-NK and B-lec V␣24J␣Q T cell receptor ␣ chains. J. Exp. Med. 188: 867–876. suggests that the NK complex and the MHC share a common ancestral region. J. Im- 9. Poggi, A., P. Costa, L. Morelli, C. Cantoni, N. Pella, F. Spada, R. Biassoni, L. Nanni, munol. 174: 3475–3483. V. Revello, E. Tomasello, et al. 1996. Expression of human NKRP1A by CD34ϩ 27. Boles, K. S., R. Barten, P. R. Kumaresan, J. Trowsdale, and P. A. Mathew. 1999. immature thymocytes: NKRP1A-mediated regulation of proliferation and cytolytic Cloning of a new lectin-like receptor expressed on human NK cells. Immunogenetics activity. Eur. J. Immunol. 26: 1266–1272. 50: 1–7.