T-cell co-stimulation through B7RP-1 and ICOS.

T-cell activation requires co-stimulation through receptors such as CD28 and antigen-specific signalling through the T-cell antigen receptor. Here we describe a new murine costimulatory receptor-ligand pair. The receptor, which is related to CD28 and is the homologue of the human protein ICOS, is expressed on activated T cells and resting memory T cells. The ligand, which has homology to B7 molecules and is called B7-related protein-1 (B7RP-1), is expressed on B cells and macrophages. ICOS and B7RP-I do not interact with proteins in the CD28-B7 pathway, and B7RP-1 co-stimulates T cells in vitro independently of CD28. Transgenic mice expressing a B7RP-1-Fc fusion protein show lymphoid hyperplasia in the spleen, lymph nodes and Peyer's patches. Presensitized mice treated with B7RP-1-Fc during antigen challenge show enhanced hypersensitivity. Therefore, B7RP-1 exhibits co-stimulatory activities in vitro and in vivo. ICOS and B7RP-1 define a new and distinct receptor-ligand pair that is structurally related to CD28-B7 and is involved in the adaptive immune response.

Long-term survival of solid organ allografts by brief anti-lymphocyte function-associated antigen-1 monoclonal antibody monotherapy.

Strategies targeting lymphocyte function-associated antigen-1 (LFA-1, CD11a/CD18) and intercellular adhesion molecule-1 (ICAM-1) have previously been shown to produce long-term survival of solid organ allografts in animals only when both CD11a and ICAM-1 are targeted for a brief (6-7 days) time or when extended (14 weeks) treatment with anti-CD11a monoclonal antibody (mAb) is administered. We show that recipient pretreatment followed by a brief (13 days) treatment course with high-dose anti-CD11a mAb alone produces long-term survival of cardiac allografts in the rigorous, nonprimarily vascularized heart allograft model in mice. This treatment regimen induces specific unresponsiveness in our model. In recipients bearing long-term beating cardiac grafts after treatment with anti-CD11a mAb, there still exists a high frequency of potentially antigen-reactive T cells in isolated peripheral blood lymphocyte fractions. Therefore, clonal deletion does not appear to explain the induction of specific unresponsiveness by treatment with anti-CD11a mAb in this model. These findings support the further investigation of the use of high-dose anti-LFA-1 mAb monotherapy in the pre- and early postoperative period to promote solid organ allograft survival.

Comparison of tidal volumes obtained by one-handed and two-handed ventilation techniques.

OBJECTIVES: To compare tidal volumes delivered by one- vs two-handed compressions of a manual resuscitation bag and assess the effects of subject characteristics on those tidal volumes. DESIGN: Subjects (108 healthcare providers from a 500-bed teaching hospital) were assigned randomly to one of two procedures: one- followed by two-handed compression or two- followed by one-handed compression. A 1-liter resuscitation bag, lung performance analyzer and Wright spirometer were used to measure tidal volume. Data collection occurred in a simulated situation. RESULTS: There was a significant difference in tidal volume delivered by one-handed (mean = 694 mL, SD = 111) vs two-handed compressions (mean = 827 mL, SD = 113). Hand size, grip strength, height and weight were correlated with tidal volumes generated by one-handed and two-handed procedures. No other subject characteristics were correlated with tidal volumes. CONCLUSIONS: Tidal volumes delivered by healthcare providers using one- vs two-handed compressions were found to be significantly different, with those delivered by two hands significantly greater than those delivered by one hand. Strength of hand grip was the best predictor of volume delivered and was more strongly correlated with volumes delivered by one rather than two hands.

sICAM-1 enhances cytokine production stimulated by alloantigen.

The leucocyte adhesion molecules lymphocyte functional antigen-1 (LFA-1; CD11a/CD18) and intercellular adhesion molecule-1 (ICAM-1; CD54) facilitate the cell-to-cell interactions which are required for the initiation of immune responses. The role of this interaction in the response to alloantigen was assessed by comparing the effects of monoclonal antibodies against these molecules to the effects of a soluble form of the ICAM-1 molecule in the mixed lymphocyte response (MLR). In contrast to the well-documented inhibitory effects of anti-ICAM-1 or anti-LFA-1 antibodies on mixed lymphocyte responses, we were unable to block these responses with the soluble form of ICAM-1 (sICAM-1). In contrast, the addition of sICAM-1 to these cultures resulted in a two- to sixfold enhancement in the T-cell proliferative response to alloantigen over the normal response. Unlike previous reports, the biological activity of sICAM-1 was not dependent on generation of a solid-phase form of the molecule. The enhanced proliferative response correlated with an increase in the level of TNF-alpha detected in the MLR supernatants and could be blocked by antibodies to TNF-alpha. sICAM-1 had no effect on proliferation or cytokine production in the absence of alloantigen. These results suggest that antibodies which block ICAM-1/LFA-1 not only block the adhesion which is required to stabilize cell-to-cell contact, but also block the costimulatory signal which is required for T-cell activation.

Transforming growth factor-beta 1 modulates the expression of class II histocompatibility antigens on human cells.

We have examined the effects of transforming growth factor-beta (TGF-beta 1) on the expression of the class II histocompatibility Ag, HLA-DR: 1) induced by human rIFN-gamma (rHuIFN-gamma) in human melanoma, Hs294T cells and 2) constitutively expressed in a subclone Hs294T cell line. The expression of HLA-DR Ag on Hs294T cells was induced by rHuIFN-gamma in a dose- and time-dependent manner with maximal levels obtained with 10 ng/ml rHuIFN-gamma after 48 h exposure. Treatment of Hs294T cells with natural porcine platelet-derived or human rTGF-beta 1 (1 to 100 ng/ml) in the presence of rHuIFN-gamma (0.1 to 10 ng/ml) reduced the percentage of cells positive for this Ag by approximately 40 to 50%, as determined by flow cytometry. This suppressive effect of TGF-beta 1 was not restricted to Hs294T cells inasmuch as rHuIFN-gamma induced HLA-DR surface Ag expression on PBMC-derived adherent cells was also significantly inhibited by TGF-beta 1. Northern blot analysis of cytoplasmic RNA extracted from Hs294T cells indicated that the decreased levels of HLA-DR cell-surface Ag correlated with decreased levels of mRNA transcripts encoding this Ag. TGF-beta 1 also effectively reduced the levels of HLA-DR mRNA in 1) cells that had been pretreated with rHuIFN-gamma and were expressing maximal levels of HLA-DR surface antigen and 2) cells that constitutively expressed HLA-DR surface Ag without exogenous rHuIFN-gamma treatment.

Characterization of the in vitro and in vivo species preference of human and murine tumor necrosis factor-alpha.

The species preference of human and murine tumor necrosis factor-alpha (TNF-alpha) was evaluated in human and murine systems for cytotoxic/cytostatic effects and receptor binding in vitro and murine systems for toxicity and antitumor activity in vivo. The in vitro cytotoxic/cytostatic effects of both species TNF-alpha on human and murine cell lines as well as the receptor binding studies using 125I-labeled recombinant human TNF-alpha demonstrated homologous species preferences. Species preference of TNF-alpha was also apparent in toxicity studies with BALB/c nu/nu and CB6F1 mice, and antitumor responses of CB6F1 mice to s.c. Meth A sarcoma implants. Moreover the growth of Meth A sarcoma implanted i.p. was not inhibited by either human or murine TNF-alpha. These results are discussed in view of the potential for underestimation of the biological potency of TNF-alpha from heterologous sources.

The effects of human immunodeficiency virus recombinant envelope glycoprotein on immune cell functions in vitro.

The effect of human immunodeficiency virus (HIV) recombinant envelope glycoprotein 120 (rgp 120) on the functions of peripheral blood mononuclear cells (PBMC) in vitro was investigated. The results demonstrate that rgp 120 used at concentrations less than 1 microgram/ml has no significant effects on PBMC function in vitro. However, the addition of 1-20 micrograms/ml of rgp 120 significantly inhibits the tetanus toxoid-induced PBMC proliferative response in a dose-related manner as determined by [3H]thymidine incorporation. The data also show that rgp 120 (5 micrograms/ml) causes up to 70% reduction in the number of immunoglobulin G-secreting cells in pokeweed mitogen-stimulated PBMC cultures. Further, rgp 120 can selectively interact with the CD4a epitope of the CD4 helper cell membrane receptor. These results indicate that microgram per milliliter levels of rgp 120 can depress certain immune functions in vitro. The significance of these findings to the pathogenesis of immunodeficiency in HIV infection remains to be determined.