Rosetting of human T lymphocytes with sheep and human erythrocytes. Comparison of human and sheep ligand binding using purified E receptor

Previous studies have shown that the purified T lymphocyte glycoprotein, cluster differentiation 2 (CD2) (also known as T11, lymphocyte function-associated antigen (LFA)-2, and the erythrocyte (E) rosette receptor) interacts with the LFA-3 molecule on human E. We have examined the interaction of the purified CD2 molecule with the T11 target structure (T11TS) molecule on sheep E, and compared the two interactions. Purified, 125I-labeled CD2 bound to sheep E and the binding was inhibited by anti-T11TS monoclonal antibody (mAb). Reciprocally, the binding of T11TS mAb to sheep E was inhibited by pretreatment of sheep E with purified CD2. High concentrations of purified CD2 aggregated sheep E, possibly by inserting into the membrane, and the aggregation was inhibited by T11TS mAb. The affinity and number of binding sites for purified CD2 on sheep and human E was found to be similar, with Ka of 9 X 10(7)/M and 6 X 10(7)/M and 9800 and 8300 CD2 binding sites/E, respectively. Thus, the human T lymphocyte CD2 molecule is a receptor that cross-reacts between LFA-3 on human E and T11TS on sheep E, suggesting that LFA-3 and T11TS are functionally homologous ligands. As measured by saturation mAb binding, there are 8100 and 3900 ligand molecules/sheep and human E, respectively. Human and sheep E have surface areas of 145 and 54 micron 2, respectively. The 3.2- to 5.6-fold higher ligand density on sheep E appears to account for the ability of sheep but not human E to rosette with certain types of human T lymphocytes.     

Antibodies against the CD44 p80, lymphocyte homing receptor molecule augment human peripheral blood T cell activation

The CD44 inhibitor Lutheran [In(Lu)]-related p80 molecule has recently been shown to be identical to the Hermes-1 lymphocyte homing receptor and to the human Pgp-1 molecule. We have determined the effect of addition of CD44 antibodies to in vitro activation assays of PBMC. CD44 antibodies did not induce PBMC proliferation alone, but markedly enhanced PBMC proliferation induced by a mitogenic CD2 antibody pair or by CD3 antibody. CD44 antibody addition had no effect upon PBMC activation induced by PHA or tetanus toxoid. CD44 antibody enhancement of CD2 antibody-induced T cell activation was specific for mature T cells as thymocytes could not be activated in the presence of combinations of CD2 and CD44 antibodies. CD44 antibody enhancement of CD2-mediated T cell triggering occurred if CD44 antibody was placed either on monocytes or on T cells. In experiments with purified monocyte and T cell suspensions, CD44 antibodies A3D8 and A1G3 augmented CD2-mediated T cell activation by three mechanisms. First, CD44 antibody binding to monocytes induced monocyte IL-1 release, second, CD44 antibodies enhanced the adhesion of T cells and monocytes in CD2 antibody-stimulated cultures, and third, CD44 antibodies augmented T cell IL-2 production in response to CD2 antibodies. Thus, ligand binding to CD44 molecules on T cells and monocytes may regulate numerous events on both cell types that are important for T cell activation. Given that recent data suggest that the CD44 molecule may bind to specific ligands on endothelial cells (vascular addressin) and within the extracellular matrix (collagen, fibronectin), these data raise the possibility that binding of T cells to endothelial cells or extracellular matrix proteins may induce or up-regulate T cell activation in inflammatory sites.     

Bromelain treatment of human T cells removes CD44, CD45RA, E2/MIC2, CD6, CD7, CD8, and Leu 8/LAM1 surface molecules and markedly enhances CD2-mediated T cell activation.

Treatment of T cells with the cysteine protease bromelain has been widely used to enhance the binding of human T cells to human E (autologous E rosettes) and has been shown to remove surface T cell CD44 molecules. Ligand binding to CD44 has been shown to markedly augment T cell activation. To study the activation potential of bromelain-treated CD44 T cells, we have compared the proliferation of sham- and bromelain-treated normal human PBMC to mitogenic CD2 mAb. We found that bromelain not only removed T cell CD44, but also removed the CD45RA isoform of CD45 as well as E2/MIC2, CD6, CD7, CD8, and Leu 8/LAM1 molecules. T cell proliferation in response to CD2 mAb was increased 325% in bromelain-treated PBMC compared to sham-treated PBMC (p < 0.005). Reciprocal treatment experiments using purified T cells and monocytes demonstrated that the enhancement of T cell CD2 activation by bromelain occurred only when T cells were treated with bromelain and was accompanied by increased adhesion of T cells to monocytes. These data demonstrate that expression of portions of the extracellular domains of the CD44, CD45RA, E2/MIC2, CD6, CD7, CD8, and Leu 8/LAM1 surface molecules are not required for CD2 activation of human T cells. Rather, the removal of these surface molecules by bromelain is associated with enhanced T cell-monocyte aggregation and enhanced CD2-mediated T cell activation. Taken together with data that CD44, E2/MIC2, CD6, and CD7 mAb inhibit CD2/lymphocyte function-associated Ag-3-mediated cellular interactions and also augment CD2-mediated triggering of T cells, these data suggest that members of the bromelain-sensitive group of surface molecules may comprise a set of CD2-associated adhesion ligands that acts in concert to modulate human T cell activation.     

A murine very late activation antigen-like extracellular matrix receptor involved in CD2- and lymphocyte function-associated antigen-1-independent killer-target cell interaction

CD2 and lymphocyte function-associated antigen (LFA)-1 are well known as T cell adhesion molecules involved in killer-target cell interactions. However, our recent study revealed that molecule(s) other than CD2 and LFA-1 might be involved in the lymphokine-activated killer (LAK) cell cytotoxicity against certain target cells. In order to characterize such unknown molecules, we established a mAb (RMV-7) which could inhibit CD2/LFA-1-independent LAK cell cytotoxicity and binding to target cells at the effector site. The Ag identified by RMV-7 appeared on splenic T cells late after mitogenic stimulation and was a noncovalently linked heterodimer composed of a 140-kDa alpha-chain and a 95-kDa beta-chain. RMV-7 blocked LAK cell binding to fibronectin (FN), fibrinogen, and vitronectin but not that to laminin or type IV collagen, indicating that the RMV-7-defined molecule is a unique extracellular matrix receptor for FN, fibrinogen, and vitronectin. One of its ligand, FN, was found on the surface of several target cells, and LAK cell cytotoxicity against them was blocked by anti-FN antibody at the target site. Similarly, cytotoxicity of a H-2d-specific CTL clone was inhibited by RMV-7 and anti-FN antibody as well. These results indicate that a unique very late activation Ag-like extracellular matrix receptor on murine CTL and LAK cells contributes to target cell binding and cytotoxicity.     

Purified lymphocyte function-associated antigen-3 (LFA-3) activates human thymocytes via the CD2 pathway

Defining the cellular and molecular mechanisms of interaction of developing thymocytes with nonlymphoid cells of the thymic microenvironment is critical for understanding normal thymus function. We have previously shown that the CD2/LFA-3 adhesion pathway is important in the interaction of thymocytes with a variety of LFA-3+ nonlymphoid thymic microenvironment cell types. Moreover, T cell activation via the CD2 (alternative, Ag independent) pathway is considered an important mechanism for intrathymic T cell proliferation. To study the relevance of CD2/LFA-3 interactions to human thymocyte activation, we have used purified LFA-3 Ag in several in vitro assays of thymocyte proliferation. Whereas LFA-3 Ag alone did not induce thymocyte proliferation, LFA-3 Ag in combination with the anti-CD2 antibody, CD2.1, and rIL-2 induced marked thymocyte proliferation. Additionally, the anti-CD28 antibody, Kolt2, could substitute for rIL-2, resulting in thymocyte activation induced by LFA-3 Ag in combination with antibodies CD2.1 and Kolt2. In both triggering systems, LFA-3 induced thymocyte activation was dependent upon the concentration of LFA-3 Ag. LFA-3 Ag-dependent thymocyte activation was directed primarily toward CD1-, mature thymocytes. Finally, intact SRBC that express the sheep homolog of LFA-3, T11TS, in combination with antibody CD2.1 and rIL-2 could also induce thymocyte activation. These data suggest that interaction of LFA-3 molecules with thymocyte CD2 molecules may provide a component of the stimulus for normal intrathymic thymocyte activation leading to thymocyte proliferation.     

Interaction of CD2 with its ligand, LFA-3, in human T cell proliferation

Recently, it has been demonstrated that lymphocyte function-associated Ag (LFA-3) is a natural ligand for CD2 and that this receptor-ligand interaction functions in cell-cell adhesion. In this report, we demonstrate that LFA-3 plays a role in T cell activation. L cells were transfected with human genomic DNA and sorted for expression of LFA-3. We demonstrate that LFA-3+ L cells, together with anti-CD3 mAb or with suboptimal doses of PHA, stimulate proliferation of human peripheral blood T cells. Furthermore, thymocyte proliferation was induced by LFA-3+ L cells and suboptimal doses of PHA. Proliferation was inhibited by mAb directed against either CD2 or LFA-3. Stimulation of thymocytes by the combination of PHA and LFA-3+ L cells resulted in the increased expression of the IL-2R, as well as of the surface Ag 4F2, transferrin receptor, and HLA-DR. These data support the conclusion that LFA-3 plays a role in CD2-dependent T cell activation. LFA-3 is widely distributed and is expressed on all APC and target cells. Thus, the ability of the CD2/LFA-3 interaction to costimulate with an anti-CD3 mAb suggests that the CD2/LFA-3 interaction may be involved not only in an Ag-independent alternate pathway of T cell activation but also in Ag-specific T cell activation.     

The CD2 ligand LFA-3 activates T cells but depends on the expression and function of the antigen receptor

The T cell Ag receptor (CD3/Ti) and the sheep E receptor (CD2) expressed on the surface of human T cells are both capable of initiating intracellular signals necessary for T cell activation. CD3/Ti interacts with Ag to initiate cellular immune responses. Although the exact function of CD2 is unknown, lymphocyte function-associated Ag 3 (LFA-3), a 55- to 70-kDa receptor expressed on a broad spectrum of hemopoietic and nonhemopoietic cells, has recently been shown to be its natural ligand. We show here that although purified multimeric LFA-3 is not capable of initiating transmembrane signaling events on its own, the combination of LFA-3 and the anti-CD2 mAb CD2.1 induces intracellular calcium increases, phosphatidylinositol second messenger generation and lymphokine secretion in the T cell leukemic line Jurkat. In order to study the signaling requirements of CD2, we compared the ability of CD2 mAb and LFA-3 to initiate activation signals in Jurkat and in three Jurkat-derived mutants. A CD3-CD2+ mutant failed to increase calcium or exhibit phosphatidylinositol hydrolysis to either the combination of agonist CD2 mAb 9-1 and 9.6 or LFA-3 and CD2.1. Reconstitution of the Ag receptor by transfection of the Ti-beta-chain restored the expression of the CD3/Ti complex and the ability to respond to either combination of CD2 ligands. However, no response to CD2 ligands was detected in a CD3+CD2+ mutant selected for signaling defects to CD3/Ti ligands. Complementation of the CD3/Ti signaling defect by cell fusion also restored competency to respond to CD2 agonists. These results demonstrate that LFA-3 under appropriate conditions can activate T cells via the CD2 complex and that this activation requires not only the cell surface expression of the CD3/Ti complex but also a functional Ag receptor pathway.     

Serologic cross-reactivity of T11 target structure and lymphocyte function-associated antigen 3. Evidence for structural homology of the sheep and human ligands of CD2

T11 target structure (T11TS) and lymphocyte function-associated antigen (LFA) 3 are the cell-surface glycoproteins on sheep and human erythrocytes (E) binding to cluster differentiation 2 (the E-receptor) on T cells in E rosette formation. Here we show that this functional cross-reactivity is most likely due to a structural homology of these molecules. A rabbit antiserum to sheep T11TS is shown to cross-react with LFA-3 in several independent assays: (a) rabbit anti-T11TS antiserum blocks the formation of E rosettes by human T cells with both autologous and xenogeneic (sheep) E by binding to the respective E; (b) the antiserum blocks the binding of anti-LFA-3 monoclonal antibody to human E; and (c) it reacts with purified LFA-3 in Western blotting. Together, these findings demonstrate that T11TS on sheep E and LFA-3 on human E are serologically related, providing further support for the notion that T11TS and LFA-3 are the sheep and human forms of the same cell interaction molecule.     

Thymocyte binding to human thymic epithelial cells is inhibited by monoclonal antibodies to CD-2 and LFA-3 antigens

With the use of cultured human thymic epithelial (TE) cells, we have previously shown that thymocytes bind to TE cells in suspension in a rosette-forming assay. To identify cell surface molecules involved in human TE-thymocyte rosette formation, we assayed a large panel of monoclonal antibodies for their ability to inhibit rosette formation. We found anti-CD-2 (LFA-2, T11), and anti-LFA-3 antibodies all inhibited binding of TE cells to thymocytes. By using indirect immunofluorescence assays, we determined that cultured TE cells were 90% LFA-3 positive and CD-2 negative, whereas thymocytes were 10% LFA-3 positive and 98% CD-2 positive. Pretreatment of TE cells with anti-LFA-3 but not anti-LFA-2 inhibited TE-thymocyte binding. In contrast, pretreatment of thymocytes with anti-CD-2 but not anti-LFA-3 antibodies inhibited TE-thymocyte binding. Thus TE cell-thymocyte binding is blocked by antibodies to the CD-2 (T11) antigen on thymocytes and by an antibody to the LFA-3 antigen on TE cells. Because the CD-2 antigen has been implicated in T cell activation, these data suggest that a natural ligand for T cell activation via the CD-2 molecule is present on human thymic epithelial cells.     

Human T lymphocyte adhesion to endothelial cells and transendothelial migration. Alteration of receptor use relates to the activation status of both the T cell and the endothelial cell

An in vitro model of T cell adhesion to human umbilical vein endothelial cells (HUVEC) and transendothelial migration was used to determine whether the activation state of the T cell or cytokine exposure of the HUVEC altered T cell-HUVEC interactions or receptor utilization. Stimulation of T cells with the activator of protein kinase C, phorbol dibutyrate (PDB) alone or in combination with the calcium ionophore, ionomycin increased their binding to HUVEC. Much of the binding of control and activated T cells to HUVEC was mediated by leukocyte function-associated Ag-1 (LFA-1) (CD11a/CD18), because mAb to either chain of this molecule inhibited binding substantially, but not completely. Activation of HUVEC with IL-1 also increased binding of T cells. Binding of control T cells to IL-1-stimulated HUVEC, however, was found to be LFA-1 independent, because mAb to CD11a/CD18 failed to block the interaction. In contrast, binding of activated T cells to IL-1-stimulated HUVEC was partially inhibited by mAb to LFA-1. Binding of activated T cells to IL-1-stimulated HUVEC also involved CD44 because this interaction was partially blocked by mAb to this determinant. When T cell migration was analyzed, it was found that the migration of PDB-activated T cells was three to four-fold more than that of control T cells. Migration through HUVEC and random migration were both enhanced by PDB stimulation. However, when the T cells were costimulated with PDB and ionomycin, migration was not increased above that of control T cells. PDB-activated T cells appeared to use LFA-1 for migration regardless of the activation status of the HUVEC, because mAb to CD11a/CD18 partially blocked their migration after binding to HUVEC. There was also a modest inhibition of PDB-activated T cell migration by mAb to CD44. In contrast, migration of control T cells involved neither LFA-1 nor CD44. Finally, binding of control T cells to high endothelial venules of peripheral lymphoid tissue was found to be CD11a/CD18 and CD44 independent, and completely inhibited by activation with either PDB or the combination of PDB and ionomycin. These results demonstrate that T cells use LFA-1 and CD44 as well as other as yet unidentified adhesion receptors for interactions with HUVEC, and that use of these adhesion receptors is mutable and related to the activation state of the T cell and cytokine stimulation of the HUVEC.     

Suppression of human lymphocyte chemotaxis and transendothelial migration by anti-LFA-1 antibody

The role of lymphocyte function-associated antigen 1 (LFA-1) in human T cell chemotaxis was investigated by using mAb specific to the beta-chain (TS1/18) (CD18) and alpha-chain (TS1/22) (CD11a) of LFA-1. T cell chemotaxis in response to IL-2 and to lymphocyte chemotactic factor (LCF) was markedly suppressed by the addition of TS1/18. TS1/22 was a less effective inhibitor than TS1/18 with only LCF stimulated responses showing significant inhibition when compared in seven different T cell preparations. Neither TS1/18 nor TS1/22 antibody inhibited random T cell migration. Control mAb to CD4 T cells failed to inhibit T cell random migration or chemotaxis. Additional studies to evaluate the adherence and migration of T cells through IL-1-stimulated human umbilical vein endothelial cell (HUVEC) monolayers showed that both TS1/22 and TS1/18 suppressed T cell migration through HUVEC, but failed to inhibit adherence of T cells to these cells. These studies indicate that LFA-1 plays a role in the migration of T cells through HUVEC and in the in vitro chemotactic response of T lymphocytes to IL-2 and LCF.     

Functional CD2 mutants unable to bind to, or be stimulated by, LFA-3.

To define epitopes on the CD2 (T11, the T cell erythrocyte receptor) molecule that are necessary for interaction with lymphocyte function-associated Ag-3 (LFA-3), we have expressed the human wild-type CD2 cDNA and mutant CD2 cDNA in a murine Ag-specific T cell hybridoma that responds to human HLA-DR Ag. Here we have expressed mutations at amino acid 91 and 92 of CD2 in the T cell hybridoma. The mutated CD2 molecules were functional in that pairs of anti-CD2 mAb that continued to bind were able to stimulate IL-2 production by the hybridomas. However, CD2 mutants with either the 91 or 92 amino acid substitution had lost the ability to bind to or be activated by either SRBC, which bear an LFA-3 homologue, or by murine L cells expressing human LFA-3. Unlike hybridomas expressing the wild-type CD2 molecule, there was no enhanced response to Ag stimulation. Taken together, these data suggest that the mutated CD2 molecules were no longer able to bind to, or to utilize, LFA-3 for activation. We have previously demonstrated that a mutation at amino acid 51 of CD2 results in loss of binding to LFA-3. Whether these two regions of CD2, discrete and separable by amino acid sequence, form one or more binding sites for LFA-3 remains to be determined.     

The hyaluronate receptor is a member of the CD44 (H-CAM) family of cell surface glycoproteins [published erratum appears in J Cell Biol 1991 Feb;112(3):following 513]

The present study was undertaken to determine the relationship between the hyaluronate receptor and CD44 (H-CAM), cell-surface glycoproteins of similar molecular weights that have been implicated in cell adhesion. In initial experiments, a panel of monoclonal antibodies directed against CD44 were tested for their ability to cross react with the hyaluronate receptor. These antibodies immunoprecipitated [3H]hyaluronate binding activity from detergent extracts of both mouse and human cells, indicating that the hyaluronate receptor is identical to CD44. In addition, one of these antibodies (KM-201 to mouse CD44) directly blocked the binding of labeled hyaluronate to the receptor and inhibited hyaluronate dependent aggregation of SV-3T3 cells. CD44 has also been implicated in lymphocyte binding to high endothelial venules during lymphocyte homing. Interestingly, the monoclonal antibody Hermes- 3, which blocks lymphocyte binding to the high endothelial venules of mucosal lymphoid tissue, had no effect on the binding of labeled hyaluronate. Furthermore, the binding of lymphocytes to high endothelial cells of lymph nodes and mucosal lymphoid tissue was not significantly affected by treatment with agents that block the binding of hyaluronate (hyaluronidase, excess hyaluronate and specific antibodies). Thus, CD44 appears to have at least two distinct functional domains, one for binding hyaluronate and another involved in interactions with mucosal high endothelial venules.     

Presentation of autoantigen by human T cells.

Activated human T cells express MHC class II and have been shown to present foreign Ag to autologous T cells. We now demonstrate that MHC class II+ T cell clones can present myelin basic protein (MBP) peptide autoantigen in the absence of traditional APC to autologous MBP reactive T cell clones. MBP peptide-pulsed T cell clones specifically stimulated autologous MBP-reactive T cell clones to flux calcium and proliferate. Activation responses were peptide epitope specific and blocked by mAb to MHC class II, indicating a TCR-mediated response. In addition, mAb to the adhesion molecules LFA-3, CD2, LFA-1, CD29, and to the tyrosine phosphatase CD45 also inhibited proliferation, indicating the involvement of T to T cell interactions. In contrast to peptide Ag, T cell clones did not respond to autologous T cells pulsed with HPLC-purified MBP, suggesting that T cells are unable to process whole MBP. However, batch-purified MBP Ag preparations containing lower m.w. breakdown products were presented by T cells, indicating that naturally occurring breakdown products of autoantigens could be presented by activated T cells in vivo. These results raise the possibility that T cell presentation of autoantigen at inflammatory sites may be important in regulation of immune responses to self Ag.     

The lymphocyte function-associated antigen (LFA)-1 and CD2/LFA-3 pathways of antigen-independent human T cell adhesion

Human cytotoxic T lymphocyte clones form conjugates with both antigen-positive and antigen-negative lymphoblastoid cells. Conjugates with antigen-negative targets form as rapidly, and are almost as frequent, as those with antigen-positive targets; both types are strong. Monoclonal antibodies against lymphocyte function-associated antigen (LFA)-1, CD2, and LFA-3 (or their Fab fragments) each consistently inhibit conjugate formation, but only partially; mixes of alpha LFA-1 with either CD2 monoclonal antibodies or alpha LFA-3 cause complete inhibition. Our previous studies have demonstrated two distinct pathways of antigen-independent conjugate (AIC) formation, one involving LFA-1 and the other involving CD2/LFA-3. The present studies showing supra-additive inhibition with mixes of Fab indicate that at least a major fraction of the conjugates involve T cells which utilize both pathways. Preincubation studies (and restricted expression for CD2) demonstrate that in the CD2/LFA-3 pathway, CD2 is critical on the effector and LFA-3 on the target and that in the LFA-1 pathway, LFA-1 is critical on the effector. Analysis of conjugate formation by primary allosensitized T cells confirms the critical findings made with T cell clones. Among a panel of antigen-negative "target" cell lines tested, there is wide variation in the number of AIC formed with cytotoxic T lymphocyte clones; this variation correlates partially with differences in level of expression of LFA-3. Both pathways of adhesion are utilized in AIC formation with all five targets tested, but there was variation between targets in the relative contribution by each pathway. Studies of inhibition of lysis (rather than conjugate formation) support the relevance of the two-pathway model to the lytic process as a whole. These studies demonstrate the general involvement of two pathways of adhesion in human T cell interactions: one involving T cell LFA-1 and the other involving T cell CD2 binding to target cell LFA-3.     

Stimulator cell-dependent requirement for CD2- and LFA-1-mediated adhesions in T lymphocyte activation by superantigenic toxins.

The staphylococcal enterotoxins and related microbial T cell mitogens stimulate T cells by cross-linking variable parts of the T cell receptor (TCR) with MHC class II molecules on accessory or target cells. We have used cloned human T cells and defined tumor cells as accessory cells (AC) to study the requirements for T cell activation by these toxins. On AC expressing high levels of CD54 (intercellular adhesion molecule-1, ICAM-1) and CD58 (lymphocyte function-associated antigen-3, LFA-3), mAb to CD2 were relatively ineffective in inhibiting the response to the toxins and antibodies to the lymphocyte function-associated antigen-1 (LFA-1) did not inhibit at all. If added together, however, these mAb inhibited the response completely. Similar results were obtained using antibodies to the target structures of CD2 and LFA-1. In contrast, on cells expressing low levels of LFA-3, mAb to LFA-1 but not to CD2 were strongly inhibitory. The same pattern of inhibition was found when these same cells were used as presenters of specific antigen to the T cells. These data show that adhesions via CD2 or LFA-1 are alternatively required for the stimulation of the T cells by superantigenic toxins and demonstrate another similarity between T cell stimulation by superantigens and by specific antigen recognition.     

Monoclonal antibodies against the CD44 [In(Lu)-related p80], and Pgp-1 antigens in man recognize the Hermes class of lymphocyte homing receptors

An 85- to 95 kDa class of lymphocyte surface molecules, defined in man by antibodies of the Hermes series, is involved in lymphocyte binding to high endothelial venules and is likely of central importance in the process of lymphocyte homing. In this report, we have examined the relationship between these Hermes-defined "homing-receptors" and two other 80 to 95 kDa lymphocyte surface molecules that have been extensively studied--CD44 [In(Lu)-related p80] defined by mAb A1G3 and A3D8, and Pgp-1 defined by antibody IM7. Our findings indicate that, in man, similar or identical glycoprotein(s) are recognized by these independently and diversely obtained antibodies. All antibodies showed identical immunohistologic patterns of reactivity on a variety of lymphoid and nonlymphoid human tissues, and demonstrated similar bands on Western blots of both crude tonsil lymphocyte lysates and highly purified Hermes-1 Ag preparations. Similarly, purified CD44/p80 Ag from RBC and human serum bound Hermes-1. Preclearing of tonsil lysates with the Hermes-1 antibody removed antigenic activity for all antibodies. Cross-blocking experiments demonstrated that A3D8, IM7 (anti-Pgp-1), and Hermes-2 antibodies recognize overlapping epitopes. Finally, expression of the epitopes defined by the Hermes-1, Hermes-3, H2-7, and H3-61 antibodies on RBC was shown to be regulated by the In(Lu) gene. These findings unify several different lines of investigation, and suggest the possibility that the CD44/Pgp-1/Hermes class of molecules may serve as cell-cell or cell-substrate adhesion/recognition elements for both hematolymphoid and non-hematolymphoid cell types.     

Is a natural ligand of the T lymphocyte CD2 molecule a sulfated carbohydrate?

Recent studies have implicated sulfated polysaccharide (SP) recognition in a range of cell adhesion systems. Inasmuch as the CD2 (E rosette receptor, T11, LFA-2) molecule of human T lymphocytes is a cell surface glycoprotein involved in the adhesion of T cells to various target cells the possibility that CD2 binds SP was investigated. It was found that E rosetting of human T lymphocytes, a phenomenon involving CD2, was readily inhibited by the SP dextran sulfate (DxS) and, to a lesser extent, by the sulfated polymer polyvinyl sulfate whereas 11 other SP had no effect on E rosetting, this effect occurring at the T cell level. mAb binding studies revealed that DxS and polyvinyl sulfate, but none of the other SP tested, inhibited the binding to T cells of the anti-CD2 mAb OKT11 and anti-T112 but augmented expression of the T113 epitope of the CD2 molecule. In contrast, DxS had little or no effect on the binding of anti-CD3, -CD4, -CD8, -Pgp-1 and WT31 (TCR alpha/beta) mAb. Direct evidence that CD2 binds DxS was demonstrated by the ability of DxS-coupled fibers to totally deplete the CD2 Ag from lysates of radiolabeled human T lymphocytes and by the quantitative recovery of the CD2 Ag in fiber eluates. Control fibers coupled with other SP bound little or no CD2. Collectively, the data indicate that the CD2 molecule specifically binds DxS and suggest that a potential target cell ligand for CD2 is a sulfated carbohydrate structure.     

The role of CD11a/CD18-CD54 interactions in human T cell-dependent B cell activation.

The role of leukocyte function-associated Ag-1 (LFA-1, CD11a/CD18) and intercellular adhesion molecule 1 (ICAM-1, CD54) interactions in human T cell and B cell collaboration was examined by studying the effect of mAb to these determinants on B cell proliferation and differentiation stimulated by culturing resting B cells with CD4+ T cells activated with immobilized mAb to the CD3 molecular complex. In this model system, mAb to either the alpha (CD11a) or beta (CD18) chain of LFA-1 or ICAM-1 (CD54) inhibited B cell responses significantly. The mAb did not directly inhibit B cell function, inasmuch as T cell-independent activation induced by formalinized Staphylococcus aureus and IL-2 was not suppressed. Moreover, DNA synthesis and IL-2 production by immobilized anti-CD3-stimulated CD4+ T cells were not suppressed by the mAb to LFA-1 or ICAM-1. Although the mAb to LFA-1 inhibited enhancement of IL-2 production by co-culture of immobilized anti-CD3-stimulated CD4+ T cells with B cells, addition of exogenous IL-2 or supernatants of mitogen-activated T cells could not abrogate the inhibitory effects of the mAb to LFA-1 or ICAM-1 on B cell responses. Inhibition was most marked when the mAb were present during the initial 24 h in culture. Immobilized anti-CD3-stimulated LFA-1-negative CD4+ T cell clones from a child with leukocyte adhesion deficiency could induce B cell responses, which were inhibited by mAb to LFA-1 or ICAM-1. These results indicate that the interactions between LFA-1 and ICAM-1 play an important role in mediating the collaboration between activated CD4+ T cells and B cells necessary for the induction of B cell proliferation and differentiation, and for enhancement of IL-2 production by CD4+ T cells. Moreover, the data are consistent with a model of T cell-B cell collaboration in which interactions between LFA-1 on resting B cells and ICAM-1 on activated CD4+ T cells play a critical role in initial T cell-dependent B cell activation.     

Human T cell activation by OKT3 is inhibited by a monoclonal antibody to CD44.

The CD44 molecule, also known as Hermes lymphocyte homing receptor, human Pgp-1, and extracellular matrix receptor III, has been shown to play a role in T cell adhesion and activation. Specifically, anti-CD44 mAb block binding of lymphocytes to high endothelial venules, inhibit T cell-E rosetting, and augment T cell proliferation induced by the CD2 or CD3-TCR pathways. We have characterized an anti-CD44 mAb (212.3) which immunoprecipitates a 90-kDa protein and is specific for CD44 as shown by peptide mapping and antibody competition studies. Interestingly, our studies with 212.3 demonstrate that this CD44-specific mAb completely inhibits T cell proliferation stimulated by the anti-CD3 mAb, OKT3. Inhibition is not a result of reduced cell viability, but is associated with 1) inhibition of IL-2 production, 2) inhibition of IL-2R expression, and 3) inhibition of OKT3-mediated increases in intracellular Ca2+ levels. In addition, 212.3 does not inhibit proliferation by the T cell mitogens PHA or PWM nor does it inhibit proliferation in a mixed lymphocyte reaction. Similar to other anti-CD44 mAb, 212.3 also augments T cell proliferation induced by mAb directed against the T11(2) and T11(3) epitopes of CD2. Thus, these studies describe a novel CD44-specific mAb (212.3) that inhibits T cell activation by OKT3 by blocking early signal transduction. Furthermore, these studies suggest that "receptor cross-talk" between the CD3-TCR complex and CD44 may regulate T cell activation.