Alloantigen recognition is preceded by nonspecific adhesion of cytotoxic T cells and target cells

A Functional Analysis on the Interspecies Interaction between Mouse LFA-1 and Human Intercellular Adhesion Molecule-1 at the Cell Level

The interaction between intercellular adhesion molecules (ICAM) and the integrin leukocyte function-associated antigen-1 (LFA-1) is crucial for the regulation of several physiological and pathophysiological processes like cell-mediated elimination of tumor or virus infected cells, cancer metastasis, or inflammatory and autoimmune processes. Using purified proteins it was reported a species restriction for the interaction of ICAM-1 and LFA-1, being mouse ICAM-1 able to interact with human LFA-1 but not human ICAM-1 with mouse LFA-1. However, in vivo results employing tumor cells transfected with human ICAM-1 suggest that functionally mouse LFA-1 can recognize human ICAM-1. In order to clarify the interspecies cross-reactivity of the ICAM-1/LFA-1 interaction, we have performed functional studies analyzing the ability of human soluble ICAM-1 and human/mouse LFA-1 derived peptides to inhibit cell aggregation and adhesion as well as cell-mediated cytotoxicity in both mouse and human systems. In parallel, the affinity of the interaction between mouse LFA-1-derived peptides and human ICAM-1 was determined by calorimetry assays. According to the results obtained, it seems that human ICAM-1 is able to interact with mouse LFA-1 on intact cells, which should be taking into account when using humanized mice and xenograft models for the study of immune-related processes.

Protein kinase C theta regulates stability of the peripheral adhesion ring junction and contributes to the sensitivity of target cell lysis by CTL

Destruction of virus-infected cells by CTL is an extremely sensitive and efficient process. Our previous data suggest that LFA-1-ICAM-1 interactions in the peripheral supramolecular activation cluster (pSMAC) of the immunological synapse mediate formation of a tight adhesion junction that might contribute to the sensitivity of target cell lysis by CTL. Herein, we compared more (CD8(+)) and less (CD4(+)) effective CTL to understand the molecular events that promote efficient target cell lysis. We found that abrogation of the pSMAC formation significantly impaired the ability of CD8(+) but not CD4(+) CTL to lyse target cells despite having no effect of the amount of released granules by both CD8(+) and CD4(+) CTL. Consistent with this, CD4(+) CTL break their synapses more often than do CD8(+) CTL, which leads to the escape of the cytolytic molecules from the interface. CD4(+) CTL treatment with a protein kinase Ctheta inhibitor increases synapse stability and sensitivity of specific target cell lysis. Thus, formation of a stable pSMAC, which is partially controlled by protein kinase Ctheta, functions to confine the released lytic molecules at the synaptic interface and to enhance the effectiveness of target cell lysis.

ADAM-15/metargidin mediates homotypic aggregation of human T lymphocytes and heterotypic interactions of T lymphocytes with intestinal epithelial cells

Intestinal epithelial cells (IEC) play an immunoregulatory role in the intestine. This role involves cell-cell interactions with intraepithelial lymphocytes that may also play a role in some enteropathies. The discovery of the RGD motif-containing Protein ADAM-15 (a disintegrin and metalloprotease-15) raises the question of its involvement in these cell-cell interactions. Cell adhesion assays were performed using the Jurkat E6.1 T cell line as a model of T lymphocytes and Caco2-BBE monolayers as a model of intestinal epithelia. Our results show that an anti-ADAM-15 ectodomain antibody inhibited the attachment of Jurkat cells on Caco2-BBE monolayers. Overexpression of ADAM-15 in Caco2-BBE cells enhanced Jurkat cell binding, and overexpression of ADAM-15 in Jurkat cells enhanced their aggregation. Mutagenesis experiments showed that both the mutation of ADAM-15 RGD domain or the deletion of its cytoplasmic tail decreased these cell-cell interactions. Moreover, wound-healing experiments showed that epithelial ADAM-15-mediated Jurkat cell adhesion to Caco2-BBE cells enhances the mechanisms of wound repair. We also found that ADAM-15-mediated aggregation of Jurkat cells increases the expression of tumor necrosis factor-alpha mRNA. These results demonstrate the following: 1) ADAM-15 is involved in heterotypic adhesion of intraepithelial lymphocytes to IEC as well as in homotypic aggregation of T cells; 2) both the RGD motif and the cytoplasmic tail of ADAM-15 are involved for these cell-cell interactions; and 3) ADAM-15-mediated cell-cell interactions are involved in mechanisms of epithelial restitution and production of pro-inflammatory mediators. Altogether these findings point to ADAM-15 as a possible therapeutic target for prevention of inappropriate T cell activation involved in some pathologies.

Anti-LFA-1 antibody postpones T-cell receptor triggering while preserving generation of regulatory T cells in T-cell receptor anti-HY transgenic mice

BACKGROUND

Anti-LFA-1 (CD11a) antibody increases allograft survival and/or induces tolerance in murine models, but its mechanisms of action remain to be elucidated.

METHODS

Rag-2-/- H-2b recipient mice, bearing a transgenic T-cell receptor specific for the male antigen HY presented by MHC class II molecule, were transplanted with a C57BL/6 (H-2b) male heart with or without administration of anti-LFA-1 antibody from days -1 to 9.

RESULTS

Treatment prevented the transient episode of acute graft rejection observed in nontreated mice and maintained a naive phenotype and proliferative characteristics comparable to that of naive transgenic lymphocytes on day 7 during treatment, with decreased IFN-gamma mRNA and increased IL-4 mRNA. On day 14, phenotype and proliferative response of lymphocytes in treated mice was comparable to those of untreated animals. Furthermore, treatment did not interfere with the generation of CD4+Vbeta6+CD25+ (Foxp3) cells that were observed in long-term nontreated tolerant mice.

CONCLUSIONS

This in vivo model demonstrates that anti-LFA-1 treatment induced a transient blockade of antigen recognition, which inhibited and postponed induction of signal 1 via the TCR and decreased the intensity of the Th1 response. Importantly, LFA-1 blockade did not disturb spontaneous generation of regulatory mechanism. This treatment would be compatible in clinical settings with other therapeutics inducing regulatory mechanisms.

ICAM-1 co-stimulates target cells to facilitate antigen presentation

Adhesion molecules are known to mediate cell-cell interactions, particularly those between T cells and antigen-presenting or target cells. Recent studies identified ICAM-1 as a co-stimulatory ligand that binds to lymphocyte function associated antigen-1 (LFA-1), thereby promoting the activation of T cells. As ICAM-1 is expressed on virtually any cell, it becomes a crucial molecule for the activation of CD8(+) T cells in the absence of co-stimulation provided by CD80 and CD86 molecules. In addition, ICAM-1 might function as cell-surface receptor, capable of initiating intracellular signaling. ICAM-1 is associated with other cell molecules, including MHC-I proteins, and our recent data show that productive engagement of ICAM-1 on target cells leads to recruitment of the MHC-I proteins to the contact area and enhances presentation of cognate peptide MHC-I complexes to cytotoxic T cells.

Induction of regular cytolytic T cell synapses by bispecific single-chain antibody constructs on MHC class I-negative tumor cells

Certain bispecific single-chain antibody constructs exhibit an extraordinary potency for polyclonal T cell engagement and target cell lysis. Here we studied the structural basis for this potency, using laser scanning confocal microscopy. Cytolytic human T cell synapses could be triggered either by addition of a specific peptide antigen or an Ep-CAM-/CD3-bispecific T cell engager (BiTE). Both kinds of synapses showed a comparable distribution of all protein markers investigated. Two other BiTEs constructed from different Ep-CAM-specific antibodies gave similar results. BiTEs could also induce lytic synapses between human T cells and a MHC class I-negative, Ep-CAM cDNA-transfected cell line resulting in potent target cell lysis. This shows that certain T cell recognition molecules on target cells are dispensable for synapse formation and BiTE activity, and suggests that BiTE-activated polyclonal T cells may ignore major immune evasion mechanisms of tumor cells in vivo, such as loss of MHC class I expression.

Major histocompatibility complex class I-intercellular adhesion molecule-1 association on the surface of target cells: implications for antigen presentation to cytotoxic T lymphocytes

Polarization and segregation of the T-cell receptor (TCR) and integrins upon productive cytotoxic T-lymphocyte (CTL) target cell encounters are well documented. Much less is known about the redistribution of major histocompatibility complex class I (MHC-I) and intercellular adhesion molecule-1 (ICAM-1) proteins on target cells interacting with CTLs. Here we show that human leucocyte antigen-A2 (HLA-A2) MHC-I and ICAM-1 are physically associated and recovered from both the raft fraction and the fraction of soluble membranes of target cells. Conjugation of target cells with surrogate CTLs, i.e. polystyrene beads loaded with antibodies specific for HLA-A2 and ICAM-1, induced the accumulation of membrane rafts, and beads loaded with ICAM-1-specific antibodies caused the selective recruitment of HLA-A2 MHC-I at the contact area of the target cells. Disruption of raft integrity on target cells led to a release of HLA-A2 and ICAM-1 from the raft fraction, abatement of HLA-A2 polarization, and diminished the ability of target cells bearing viral peptides to induce a Ca(2+) flux in virus-specific CTLs. These data suggest that productive engagement of ICAM-1 on target cells facilitates the polarization of MHC-I at the CTL-target cell interface, augmenting presentation of cognate peptide-MHC (pMHC) complexes to CTLs. We propose that ICAM-1-MHC-I association on the cell membrane is a mechanism that enhances the linkage between antigen recognition and early immunological synapse formation.

Correlation of a dynamic model for immunological synapse formation with effector functions: two pathways to synapse formation

During antigen recognition by T cells different receptors and ligands form a pattern in the intercellular junction called the immunological synapse, which might be involved in T-cell activation. Recently, a synapse assembly model has been proposed, which enables the calculation of the propensity for synapse assembly driven by membrane-constrained protein binding interactions. We bring together model predictions of mature synapse assembly with data on the dependence of T-cell responses on T-cell receptor (TCR)-MHC-peptide (pMHC) binding kinetics. Predictions of mature synapse assembly, based on TCR-pMHC binding kinetics, correlate well with observed cytokine responses by T cells bearing the relevant TCR but not with cytotoxic T lymphocyte-mediated killing. We discuss the suggested different role for the synapse in pre- and post-nuclear activation events in T cells. The view of immunological synapse assembly given here emphasizes the importance of both the on and off rates for the TCR-pMHC interaction and in this context recent data on a positive role for analogs of self-peptides in synapse assembly is considered.

Antibodies for transplantation

The use of antibodies in transplantation has become a clinical reality. Antibodies have been used to both dampen the recipient's immune response and to obscure the immunogenicity of the donor graft. Traditionally, antibodies have been administered to the transplant recipient to transiently inactivate the host's T cells, the lymphocytes responsible for recognizing and attacking foreign proteins, cells, and tissues. Antibodies can also be used to eliminate any highly immunogenic passenger cells from a donor graft prior to transplantation, and antibodies can mask or conceal antigens present on donor cells that might trigger rejection.

Making a little affinity go a long way: a topological view of LFA-1 regulation

Lymphocytes utilize adhesion to navigate in the body and to transiently interact with a variety of potential antigen presenting cells. Interactions of adhesion molecules are governed by the law of mass action and the less understood rules of apposed biological membranes. Biochemical parameters such as adhesion molecule affinity only tell part of the story. Factors such as lateral mobility, membrane alignment and cytoskeletal interactions are equally important in determining the final outcome. Therefore it is important to determine mechanisms by which the properties of cell membranes and the cytoskeleton reinforce or hinder adhesion molecule interactions. Work from my lab has shown that one mechanism by which lymphocyte adhesion molecules cooperate is to align adhering membranes with nanometer precision. Here, I discuss a model for LFA-1 regulation that is dependent on three independent processes: LFA-1 lateral mobility, ligand induced generation of a small amount of high affinity LFA-1 and local membrane alignment. I propose that coordination of these processes allows rapid interconversion between stable adhesion and detachment.

Staphylococcal enterotoxin B-specific adhesion of murine splenic T cells to a human endothelial cell line

The presence of a putative autoantigen of autoimmune disorder in a target organ may cause accumulation of specific T cells in the inflammatory region. One of the mechanisms of such accumulation involves the migration of specific-circulating T cells through the endothelial cells into the target lesion. The presence of only a few specific T cells responsive to a putative autoantigen has hampered the investigation of specific migration of circulating T cells to the target organ. We used a superantigen to investigate specific T-cell adhesion to endothelial cells, because it stimulates a large proportion of T cells with particular V beta elements and adhesion of T cells to the endothelium is a vital step in the migration process. Adhesion of murine T cells to the human endothelial cell line, EA.hy926, was specifically increased in the presence of staphylococcal enterotoxin B (SEB). The increase was interferon-gamma (IFN-gamma)-dependent, and consisted mainly of CD4+ T cells. V beta 8.1,2+ T cells preferentially adhered to endothelial cells in the presence of SEB compared with V beta 6+ T cells. Pretreatment of endothelial cells with SEB increased the adherence of V beta 8.1,2+ T cells, while anti-human leucocyte antigen (HLA)-DR and -DQ antibodies inhibited the increased adherence of V beta 8.1,2+ T cells. Our results demonstrate that increased T-cell adhesion to endothelial cells is SEB specific, and that the specificity is dependent on major histocompatibility complex (MHC) class II molecules expressed on endothelial cells and on the recognition of the SEB-MHC class II complex by V beta 8.1,2+ T cells.

The law of mass action governs antigen-stimulated cytolytic activity of CD8+ cytotoxic T lymphocytes

An analysis of the initial antigen-recognition step in the destruction of target cells by CD8+ cytolytic T lymphocytes (CTLs) shows that a relationship in the form of the law of mass action can be used to describe interactions between antigen-specific receptors on T cells (TCRs) and their natural ligands on target cells (peptide-major histocompatibility protein complexes, termed pepMHC complexes), even though these reactants are confined to their respective cell membranes. For a designated level of lysis and receptor affinities below about 5 X 10(6) M-1, the product of the required number of pepMHC complexes per target cell ("epitope density") and TCR affinity for pepMHC complexes is constant; therefore, over this range TCR affinities can be predicted from epitope densities (or vice versa). At higher receptor affinities ("affinity ceiling") the epitope density required for half-maximal lysis reaches a lower limit of less than 10 complexes per target cell.

Performance of CD3xCD19 bispecific monoclonal antibodies in B cell malignancy

Bispecific monoclonal antibodies, with a dual specificity for tumor associated antigens on target cells and for surface markers on immune effector cells, have been shown (in vitro) to be effective in directing and triggering effector cells to kill target cells resulting in target cell lysis. Bispecific monoclonal antibodies (BsAb) against the CD3 antigen on T cells and the CD19 antigen on B cell were developed. Data obtained by in vitro experiments might indicate that clinical responses in BsAb immunotherapy, will only be obtained in patients with minimal tumor load, and may need additional T cell stimulation via cytokines such as IL-2. Although these experiments have shown us their limitations, they also include the promise of BsAb-directed immunotherapy in B cell malignancy as further demonstrated during a Phase I trail, showing little toxicity. Clearly, much remains to be done before this BsAb is routinely used for therapy, but, the results presented show that the CD3xCD19 BsAb has a potential as a therapeutic agent in B cell malignancy. This report describes the experiments performed to test a new immunotherapeutic approach for the treatment of B cell malignancy. Bispecific antibodies are described that can target cytotoxic T cells to tumor cells and elicit a cytolytic action towards these cancer cells.

Immunosuppressive and anti-inflammatory properties of interleukin 10

Interleukin 10 (IL-10) indirectly prevents antigen-specific T-cell activation, which is associated with downregulation of the antigen presentation and accessory cell functions of monocytes, macrophages, Langerhans cells and dendritic cells. In addition, IL-10 inhibits T-cell expansion by directly inhibiting IL-2 production by these cells. These properties of IL-10, together with its capacity to downregulate the production of proinflammatory cytokines and chemokines by activated monocytes, polymorphonuclear leucocytes and eosinophils, indicate that IL-10 is a potent immunosuppressant in vitro. IL-10 has similar activities in vivo. It inhibits lipopolysaccharide or staphylococcal enterotoxin B induced lethal shock in mice. In addition, IL-10 deficient mice develop chronic inflammatory bowel disease, which could be reduced, or prevented by IL-10 treatment. IL-10 also prevented the development of colitis in a SCID mouse model. Collectively, these data indicate that IL-10 has great potential therapeutical utility in the treatment of diseases, such as chronic inflammation, autoimmune diseases, transplant rejection, graft-versus-host disease and sepsis.

Occurrence and a possible mechanism of penetration of natural killer cells into K562 target cells during the cytotoxic interaction

The cytotoxic interaction between cloned human Natural Killer (NK) cells and K562 target cells was studied using confocal laser scanning microscopy (CLSM) and conventional fluorescence microscopy. We observed, using fixed as well as living cells, the occurrence of (pseudo) emperipolesis during the interaction. About 30% of conjugated NK cells penetrated, partly or completely, into the target cells (in-conjugation). Virtually all in-conjugated target cells exhibited polymerized actin. Killer cells of in-conjugates were frequently seen approaching the target cell nucleus or aligning along it. If the cytotoxic process was inhibited by the absence of calcium neither actin polymerization nor in-conjugation were observed. A kinetic study showed that in-conjugation starts somewhat later than actin polymerization but still within a few minutes after addition of calcium to conjugates previously formed in the absence of calcium. The presence of cytochalasin D (an inhibitor of actin polymerization) completely inhibited in-conjugation and partly reduced the cytotoxic activity. Zinc ions (endonuclease inhibition) inhibited in-conjugation and decreased the total number of target cells with polymerized actin in a concentration dependent manner. Cytotoxic activity was also reduced but not as efficiently as in-conjugation. Our study demonstrates that in-conjugation represents a significant fraction of the cytotoxic interaction. The results indicate that it may be a consequence of an actin polymerization and endonuclease activity dependent part of a cytotoxic mechanism.

Costimulation by purified intercellular adhesion molecule 1 and lymphocyte function-associated antigen 3 induces distinct proliferation, cytokine and cell surface antigen profiles in human "naive" and "memory" CD4+ T cells

Activation of resting human CD4+ "naive" (CD45RA+CD45RO-) and "memory" (CD45RA-CD45RO+) T cells requires costimulatory signals in addition to engagement of the T cell receptor/CD3 complex (TCR/CD3). The adhesion pathways mediated by lymphocyte function-associated antigen 1/intercellular adhesion molecule 1 (LFA-1/ICAM-1) and CD2/LFA-3 are capable of providing such costimulatory signals. Our work shows that these costimulatory adhesion pathways are critically involved in regulation of T cell differentiation/maturation. Evidence for subset-specific costimulatory requirements is demonstrated by the finding that only memory CD4+ T cells were costimulated by LFA-3, whereas both naive and memory CD4+ T cells were costimulated by ICAM-1. In addition, these costimulatory adhesion pathways regulated reciprocal cytokine secretion patterns for interleukin 5 (IL-5) and granulocyte/macrophage colony-stimulating factor (GM-CSF). Repeated costimulation of CD4+ memory T cells with LFA-3 led to secretion of high levels of IL-5, while repeated costimulation with ICAM-1 induced high levels of secreted GM-CSF. Significant interferon gamma (IFN-gamma) production was observed with either of the costimulatory ligands. Extensive cell surface analysis of these in vitro cultures of peripheral blood derived memory CD4+ T cells, with monoclonal antibodies obtained from the 5th Leucocyte Typing Workshop, revealed differential expression of a singular antigen, CD60. This antigen was preferentially expressed on LFA-3-costimulated cells suggesting a positive correlation between CD60 expression and a T helper type 2-like cytokine profile. In conclusion, this report demonstrates a new functional role for costimulatory adhesion molecules in regulating differential cytokine secretion in human memory CD4+ T cells.

Molecular analysis of antigen-independent adhesion forces between T and B lymphocytes

The low-affinity interactions underlying antigen recognition by T-cell receptors (TCRs) are thought to involve antigen-independent adhesion mechanisms. Using a hydrodynamic approach, we found that antigen-independent adhesion occurred between human B cells and resting T cells in a transient and temperature-dependent fashion. The mean cell-cell adhesion force was 0.32 x 10(-9) N and was generated by similar contributions (0.16 x 10(-9) N) of the LFA-1- and CD2-dependent adhesion pathways. After T-cell stimulation with a phorbol ester, the force contributed by LFA-1 was drastically increased, while that of CD2 was unaffected. We propose that weak receptor-mediated adhesion initiates antigen-independent intercellular contacts required for antigen recognition by the TCR and is upregulated following TCR engagement. The method used permits adhesion forces between living cells to be resolved at the molecular level and should prove valuable for the rapid assessment of interaction forces between various types of cells and cell-sized particles.

Role of LFA-1/ICAM-1 in interleukin-2-stimulated lymphocyte proliferation

Major adhesion routes between lymphoid cells involve the receptor/ligand pairs LFA-1/ICAM-1 and CD2/LFA-3, in addition to VLA or CD44 molecules. In this study we evaluated the role of these adhesion receptors in the proliferative response of lymphoid cells to interleukin-2 (IL-2). Blocking studies were performed with a panel of monoclonal antibodies (mAb) directed against these adhesion molecules. Selective inhibition of recombinant (r)IL-2-induced cell proliferation was observed with mAb directed against the alpha or beta subunit of LFA-1 or to its ligand ICAM-1. Interestingly, rIL-2-induced proliferation was also inhibited by NKI-L16, and anti-1 alpha antibody known to enhance cell-cell interaction. Resting lymphocytes were preferentially susceptible to the inhibition, particularly in an early phase of culture and when stimulated with a relatively low dose of rIL-2. By using mAb that specifically could block distinct rIL-2 activation pathways, LFA-1/ICAM-1 interaction was found to be required for p55 IL-2 receptor (IL-2R)-mediated interaction of rIL-2 with its high-affinity receptor, but not for p75 IL-2R-mediated responses. Furthermore, it was shown that the rIL-2 response of T lymphocytes, but not of natural killer cells, was dependent on LFA-1/ICAM-1 interaction. This suggests that LFA-1/ICAM-1 interaction is required for an optimal rIL-2 response of cells capable of IL-2 secretion. Our data provide evidence for the hypothesis that adhesion receptor-directed release of IL-2 may result in a locally high concentration of IL-2 that triggers high-affinity IL-2R signaling and up-regulates p55 IL-2R to enhance cytokine responsiveness.

Local antitumour treatment in carcinoma patients with bispecific-monoclonal-antibody-redirected T cells

In a pilot clinical study carcinoma patients with malignant ascites or pleural exudates have been treated locally with autologous lymphocytes activated ex vivo and redirected towards tumour cells with bispecific monoclonal antibodies. BIS-1, the bispecific monoclonal antibody used in this study, combines specificity against a tumour-associated antigen, AMOC-31, present on carcinomas, with a specificity against the CD3 complex on T lymphocytes. Patients selected for treatment had malignant pleural or peritoneal effusions. Treatment consisted of isolating autologous peripheral blood lymphocytes, ex vivo activation, incubation with bispecific monoclonal antibodies and injection at the effusion site of these BIS-1-redirected lymphocytes. To evaluate the effects of the bispecific monoclonal antibody, five patients received treatments with activated lymphocytes without bispecific antibodies. Effusion samples taken before and at various times after treatment were analysed by immunocytology and for the presence of the soluble factors carcinoembryonic antigen (CEA), interleukin-6 (IL-6), tumour necrosis factor (TNF), C-reactive protein and soluble CD8. In this way both immune activation and anti-tumour activity could be monitored. Conjugate formation between tumour cells and activated lymphocytes was seen as soon as 4 h after injection of BIS-1-redirected activated lymphocytes, followed by a disappearance or reduction of tumour cells after 24-48 h. In parallel with this, the soluble tumour marker CEA decreased in the effusion fluid following injection with the BIS-1-redirected lymphocytes. Furthermore, a steep increase in local granulocyte numbers was observed in the effusion fluid, which reached a maximum 24-48 h after the start of the treatment. Also levels of IL-6 and TNF were greatly elevated. The data suggest that the treatment induces both antitumour activity and a strong local inflammatory reaction. This is accompanied by no or only minor local and systemic toxicity, i.e. mild fever, which disappeared as the local inflammatory reaction diminished 48-72 h after treatment.

Cellular recognition and HLA restriction of a midsequence HBsAg peptide in hepatitis B vaccinated individuals

Vaccination with native HBsAg results in both a humoral and a cellular immune response in humans. In individuals who responded to vaccination, the HBsAg (S region) specific response, as measured by cell proliferation, diminished significantly after 12 weeks, a time when the antibody response was still vigorous. Reduced and nonreduced HBsAg were equivalent in eliciting lymphocyte proliferation. Anti-MHC class II monoclonal antibodies were used in blocking studies to demonstrate that anti-HLA-DR but not anti-HLA-DQ or anti-HLA-DP inhibited specific lymphocyte proliferation to HBsAg. Both the monomer (reduced) and dimer (nonreduced) forms of an immunodominant midsequence HBsAg peptide (amino acid residues 139-146) produced lymphocyte proliferation roughly comparable to that induced by whole HBsAg in 6 of 7 responders immunized with whole HBsAg and the peptide-induced proliferation was blocked by anti-HLA-DR but not by anti-HLA-DP antibodies. These results suggest that HBsAg p 139-146 is a major immunodominant peptide of HBsAg and is restricted by HLA-DR.

Cell-cell adhesion by homophilic interaction of the neuronal recognition molecule axonin-1

The axonal surface glycoprotein axonin-1, which occurs both as a glycosyl-phosphatidylinositol-anchored membrane-bound form and a secreted form, promotes neurite outgrowth and is thought to be involved in axon-guidance mechanisms in the developing nervous system. Recently, we have demonstrated that the neurite-outgrowth-promoting activity of axonin-1, presented as a substratum for cultured neurons, is mediated by a heterophilic interaction with the axonal glycoprotein neuronglia cell-adhesion molecule (Ng-CAM). Here we present evidence for homophilic (like-like) binding among axonin-1 molecules. Axonin-1 was heterologously expressed in myeloma cells. Clonal cell lines, with exposed membrane-bound axonin-1 at their surface, formed large multicellular aggregates. Incubations of transfected and parental myeloma cells, under a series of different conditions, revealed homophilic axonin-1/axonin-1 interactions across the intermembrane space as the molecular mechanism promoting stable cell-cell contacts. Using structural and functional characterisation, recombinant axonin-1 was very similar to native axonin-1, suggesting that homophilic axonin-1 interactions are also established in neurons. The capability of axonin-1 to interact with both Ng-CAM and other axonin-1 molecules might contribute to the formation of macromolecular networks at contact sites of growth cones and axons, comprising molecules of both membranes, and thus represent a mechanism for regulating neurite outgrowth and pathfinding.

Role of cAMP in regulating cytotoxic T lymphocyte adhesion and motility

We investigated the functional role of the cAMP pathway in human cytotoxic T lymphocyte (CTL)-target interaction. Pharmacological increase of intracellular cAMP concentration ([cAMP]i) inhibits killing, especially at low effector-to-target ratios, suggesting an inhibitory effect on CTL recycling. We show that this inhibitory effect is primarily at the level of conjugate formation. Pharmacological increase in [cAMP]i, as well as treatment with cytochalasin D, results in a "rounding up" of the CTL and inhibition of the dramatic changes in shape that occur when a CTL forms a conjugate, even with an irrelevant target. In addition, pharmacological increase in [cAMP]i affects the cytoskeleton of the CTL since it induces a decrease of filamentous actin, as detected by flow cytometry on phalloidin-stained CTL, and a stabilization of microtubules, as detected by increased resistance to the disrupting action of nocodazole. In mature CTL (but not in their immature precursors), T cell receptor triggering by specific targets results in a measurable increase in cAMP levels and strongly synergizes with adenylyl cyclase activators such as prostaglandin E2, cholera toxin and forskolin. We suggest that T cell receptor triggering may induce accumulation of cAMP that interferes with cytoskeleton function and, thus, terminates CTL secretion and adhesion. These effects of cAMP are rapidly reversible and may regulate CTL recycling.

Skewing to the LFA-3 adhesion pathway by influenza infection of antigen-presenting cells

The effect of influenza (FLU) infection on heterotypic conjugate formation between antigen-presenting cells and T lymphocytes has been studied with FLU-specific T cell clones and FLU-infected B-lymphoblastoid cells (B-LCL). Conjugate formation between FLU-infected B-LCL (FLU+ B-LCL) and T cells was found to be consistently enhanced in comparison with peptide-sensitized or uninfected B-LCL. Treatment of B-LCL with exogenous neuraminidase (NA-NAse) similarly enhanced conjugate formation indicating that increased conjugate formation may be mediated by the viral neuraminidase. Monoclonal antibody blocking experiments revealed that the contribution by CD2/LFA-3 is increased relative to that of LFA-1/ICAM-1 in conjugates between FLU+ B-LCL or NANAse-treated B-LCL and T cell clones. In contrast, both pathways of adhesion contributed equally to conjugate formation between peptide-sensitized B-LCL or control B-LCL and T cell clones. Thus, FLU infection causes increased conjugate formation between antigen-presenting cells and T cells and skews towards CD2/LFA-3-dependent adhesion, independent of T cell receptor signalling.

Topology and affinity of T-cell receptor mediated recognition of peptide-MHC complexes

Significant progress has been made on several long-standing issues regarding T-cell receptor mediated recognition of antigen-MHC complexes. For one, early data suggest that the affinity of the T-cell receptor for the peptide-MHC complex is extremely low, with a KD of approximately 10(-4)-10(-5)M, much weaker than most antibody-antigen interactions. The fact that this affinity is lower than that of some T-cell adhesion molecules for their ligands could have important implications for immune surveillance. A second area of interest is the topology of T-cell receptor recognition; evidence of direct contact between the third complementarity determining region of the T-cell receptor and peptide determinants has been obtained. In addition, the orientation of the T-cell receptor with respect to several antigen-MHC complexes has been predicted. They suggest that whereas most or all peptides seem to bind in the same orientation in both class I and class II MHC molecules, the orientation of the T-cell receptor over the peptide-MHC complex may not be fixed.

CD2/LFA-3 or LFA-1/ICAM-1 but not CD28/B7 interactions can augment cytotoxicity by virus-specific CD8+ cytotoxic T lymphocytes

It is well established that adhesion molecules are required for interaction between cytotoxic T lymphocytes (CTL) and target cells. Two adhesion pathways, CD2/LFA-3 and LFA-1/ICAM-1 can support cytotoxicity by allospecific CD8+ CTL. In this study, it was investigated whether these adhesion pathways can be utilized independently by influenza virus-specific HLA-A2-restricted CTL clones. It was furthermore examined whether the CD28/B7 pathway can augment virus-specific CTL activity. To this end, seven CD8+ CTL clones were established that were specific for a peptide encompassing positions 59 to 68 (p[59-68]) of the influenza virus matrix protein. These seven clones apparently originated from different precursors, as they utilized different V alpha and V beta or J alpha gene segments. Six of seven clones were able to lyse mouse L cells co-transfected with HLA-A2 and either LFA-3 (LA2/LFA-3) or ICAM-1 (LA2/ICAM-1) in the presence of p[59-68] but did not lyse L cells that expressed only HLA-A2 and peptide. Three of the most cytotoxic clones were selected for further analysis. The cytotoxicity of the clones against LA2/LFA-3 cells was blocked by anti-LFA-3 and anti-CD2 monoclonal antibodies (mAb), while these antibodies did not affect cytotoxicity against LA2/ICAM-1 cells. Likewise, the activity against LA2/ICAM-1 was blocked only by anti-LFA-1 and ICAM-1 mAb. These clones were unable to lyse L cells co-transfected with HLA-A2 and B7, the counter structure of CD28, despite the fact that these clones expressed CD28. These data indicate that CD8+ virus-specific CTL can utilize either the CD2/LFA-3 or the LFA-1/ICAM-1 adhesion pathway. The CD28/B7 pathway seems not to be required for cytotoxicity mediated by activated virus-specific CTL.

Mechanisms of induction of primary virus-specific cytotoxic T lymphocyte responses

We have investigated the ability of various antigen-presenting cell (APC) types to induce primary anti-viral cytotoxic T lymphocyte (CTL) responses by single in vitro stimulation. Of these APC types, only dendritic cells (DC) and RMA-S lymphoma cells could induce primary CTL responses, but by divergent mechanisms. DC were capable of generating primary virus-specific CTL, either by presenting viral peptide or processed infectious virus. In contrast, RMA-S cells could not present endogenous antigen, e.g. after virus infection, but this cell line very efficiently presented exogenous viral peptides to induce primary virus-specific CTL in vitro. Spleen cells, lipopolysaccharide-induced B cell blasts or the non-mutated RMA cells did not have the ability to trigger unprimed T cells by single in vitro stimulation. We have investigated several characteristics important for primary CTL response induction by DC and RMA-S cells (summarized in Fig. 6). Primary CTL response induction by DC or RMA-S cells was blocked by anti-LFA-1 or anti-CD8 monoclonal antibodies (mAb). DC rapidly aggregated with unprimed T cells, which was independent of LFA-1 and CD8 molecules. RMA-S cells did not form conjugates with unprimed T cells. Despite their abundant major histocompatibility complex (MHC) class I cell-surface expression, DC did not bind much exogenously added viral peptide. In contrast, the MHC class I molecules on RMA-S cells bound a large quantity of exogenously administered peptide. Powerful adhesion by DC and high expression of relevant MHC/peptide complexes on RMA-S cells are important features in the initial contact with unprimed T lymphocytes. In a later stage of contact, both DC and RMA-S cells activate LFA-1 (and CD8) molecules at the T cell surface to strengthen and maintain the contact between T cell and APC.

Role of the adhesion molecule lymphocyte function associated antigen 1 in toxic shock syndrome toxin 1-induced tumor necrosis factor alpha and interleukin-1 beta secretion by human monocytes

We previously demonstrated that the induction by staphylococcal toxic shock syndrome toxin 1 (TSST-1) of tumor necrosis factor alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) secretion by human monocytes requires direct T cell-monocyte contact. In the present study, a role for the adhesion molecule lymphocyte function associated antigen 1 (LFA-1) in TSST-1-induced cytokine secretion by human monocytes among 12 normal healthy donors was investigated. Monoclonal antibodies to the alpha chain (anti-CD11a) and to the beta chain (anti-CD18) of LFA-1 significantly inhibited TSST-1-induced TNF-alpha and IL-1 beta secretion (P < 0.025; Wilcoxon signed-rank test, two tailed), while a control monoclonal antibody directed against the monocyte CD14 antigen had no effect. These results suggest that LFA-1 may play an important role in the secretion of TNF-alpha and IL-1 beta by TSST-1-stimulated human monocytes, likely by promoting cell-cell adhesion between monocytes and lymphocytes.

Expression of intercellular adhesion molecule 1 (ICAM-1) during the development of invasion and/or metastasis of gastric carcinoma

In this study, using two-color flow-cytometric analysis, we examined the expression of histocompatibility locus antigens (HLA) classes I and II, and intercellular adhesion molecule 1 (ICAM-1) in 10 cases of normal gastric mucosa, 13 cases of primary carcinoma on the stomach, 16 cases of metastatic carcinoma from malignant ascites in patients with gastric carcinoma and 14 samples of their cultured carcinoma cells. Compared with normal gastric mucosa, HLA class I were highly expressed in a considerable number of tumor cells in each experimental group. The expression of HLA class II tended to reduce in the order of normal gastric mucosa, primary gastric carcinoma and peritoneal-effusion-associated carcinoma. Altogether, 85.7% of cases of cultured tumor cells showed abrogation and loss of HLA class II. The ICAM-1 molecule was not detected on normal gastric epithelial cells. In few cases, carcinoma cells from large volumes of tumor located in the stomach showed detectable amounts of ICAM-1. On the other hand, all of the metastatic carcinoma cells from peritoneal effusions showed a high level of expression of the ICAM-1 molecule. The expression of ICAM-1 on adenocarcinoma cells was maintained and/or augmented by in vitro cultivation with tumor-infiltrating lymphocytes (TIL). Furthermore, two-color fluorescence-activated cell sorting analysis of TIL revealed that significant correlation was observed between the expression of ICAM-1 and the degree of TIL, composed mainly of CD3+ T cells including CD8+CD11b-, CD8+CD28+, CD8+S6F1+ and CD4+Leu8+, and CD57+CD16- and CD57+CD16+ NK cells, and HLA-DR+LeuM3+ macrophages.

Can hepatocytes serve as 'activated' immunomodulating cells in the immune response?

During the last few years, there has been a growing evidence that hepatocytes are not merely 'passive' target cells for immunological attack by effector T-cells, but may play a more 'active' role in the initiation and perpetuation of the immune response. Immune modulators released by inflammatory cells at the site of inflammation, as well as the eliciting antigen itself, are able to modulate the phenotype of hepatocytes. This would result in abnormal cytokine production and/or cytokine/receptor expression, as well as active synthesis and display of surface immune 'activation' markers and adhesion molecules, which act as co-stimulatory signals for T-cell activation. These accessory functions involve multiple molecular pathways of cell-cell interactions, which in turn will enable hepatocytes to play a role as 'accessory' cells in both the afferent and efferent arms of the cell-mediated immune response.

Cytolytic T lymphocytes: an overview of their characteristics

Cloned T cells have been useful for assessing the lytic potential of distinct T cell subsets and for determining the relative contribution of different effector mechanism involved in the lytic process. Alloreactive CD8+ murine T cell clones and cloned murine CD4+ TH1 and TH2 T cells reactive with nominal antigen (ovalbumin) lysed nucleated target cells bearing antigen or coated with anti-CD3 monoclonal antibody in a short term 51Cr-release assay. These clones were also evaluated for their ability to lyse efficiently sheep erythrocyte (SRBC) target cells coated with anti-CD3 mAb by a mechanism (presumably involving membrane damage) that does not involve nuclear degradation. Three patterns of lysis were observed: CD8+ and some CD4+ TH2 effector cells lysed efficiently nucleated target cells and anucleated SRBC coated with anti-CD3 mAb. However, CD4+ TH1 (and a few TH2) T cells which lysed nucleated target cells bearing antigen or coated with anti-CD3 mAb did not lyse efficiently the SRBC coated with anti-CD3 mAb. One CD4 bearing TH2 cell failed to lyse efficiently either nucleated target cells or anucleated SRBC coated with anti-CD3 mAb. These results indicate that both TH1 and TH2 clones have lytic capabilities. Furthermore, they suggest that some but not all TH2 murine T cell clones have lytic characteristics similar to those of conventional CD8+ CTL. However, it is not certain how these patterns of lysis of target cells in vitro relates to the capacity of CTL to lyse such target cells in vivo.

Both LFA-1-positive and -deficient T cell clones require the CD2/LFA-3 interaction for specific cytolytic activation

We investigated the capacity of T lymphocytes from a leukocyte adhesion-deficient (LAD) patient to respond to alloantigen. Leukocytes of this patient completely lacked LFA-1 surface expression due to the absence of mRNA coding for the LFA-1 beta chain. Despite the absence of LFA-1, T lymphocytes obtained from this patient, cultured with allogeneic stimulator cells (lymphoblastoid B cells JY), were capable of lysing JY cells. Furthermore, two T cell clones (one CD4+ and one CD8+), generated from this lymphocyte culture, specifically lysed the allogeneic lymphoblastoid JY cells. The cytolytic capacity of LFA-1-negative T lymphocytes and T cell clones was comparable to that of control LFA-1-positive T cells with allospecificity against JY. Detailed analysis of the CD4 positive and LFA-1-negative T cell clone demonstrated that it specifically recognized HLA-DQ. Antibody inhibition studies showed that the CTL/target cell interaction was mediated through the CD2/LFA-3 adhesion pathway. LFA-1 expressed by the target cells did not participate in the CTL/target cell conjugate formation and contributed only minimally to the cytotoxic activity. Moreover, when allogeneic LFA-1-deficient B cells, bearing the appropriate HLA-DQ alloantigen, were used as target cells, significant levels of specific cytotoxicity were measured, further excluding a role for LFA-1 in this interaction. The adhesion molecules, VLA-4, CD44 and L-selectin (LECAM1) were not involved. These results demonstrate that LFA-1-negative T lymphocytes can exert allospecific cytotoxicity and that CTL/target cell contact is mediated through the CD2/LFA-3 route. This observation may explain in part why in LAD patients viral infections, cleared largely by T cells, are less frequently observed than bacterial infections, in which phagocytic cells play a major role.

Antigen-receptor complex stimulation triggers protein kinase C-dependent CD11a/CD18-cytoskeleton association in T lymphocytes

Although it is well accepted that intercellular adhesion involving the CD11a/CD18 (LFA-1) complex is critical in a wide array of T cell- dependent processes, recent demonstrations of an LFA-1 high avidity state, induced by triggering the T cell receptor (TCR) complex, has raised questions about the intracellular signals generated and molecular events leading to effective cell coupling, as well as their orderly sequence. In this study, we assessed the effects of T cell activation on the actin-based cytoskeleton, and LFA-1, as well as their interaction. Crosslinking the TCR complex with anti-CD3 mAb resulted in actin polymerization and colocalization with LFA-1, as detected by fluorescence microscopy. This association was confirmed by immunoprecipitating LFA-1 from the detergent insoluble, cytoskeletal- associated membrane fraction after TCR crosslinking. These consequences were inhibited by the protein kinase C (PKC) inhibitor staurosporine or by PKC desensitization, as was a transient CD11a hyperphosphorylation, induced by monoclonal anti-CD3. Furthermore, a small percentage of beta 2-deficient T cells maintained the ability to rearrange the cytoskeleton in response to TCR complex activation, with F-actin-VLA4 colocalization. These results provide evidence that the important consequences of TCR-induced signal transduction include a PKC-dependent cytoskeletal rearrangement, involving an association between leukocyte integrins and F-actin. We discuss the implications of these findings with respect to effective T cell functions.

Cell surface oligosaccharide modulation during differentiation: VI. The effect of biomodulation on the senescent and neoplastic cell phenotype

These investigations test the hypothesis developed previously, that there are biomolecules which control and integrate cellular differentiation. Our specific interest in cellular differentiation lies in the area of what we refer to as basal or primitive cellular differentiation mechanisms. These mechanisms are common to all cells, and are required for simple recognition and growth regulation. We have investigated two models, the IMR-90 human fetal lung fibroblast model as a representative of normal growth control, and the CG model, canine glioma cells, a transplantable growth transformed cell line. These two models represent normal, and aberrant cellular differentiation control. In previous studies we have shown that the arrangement of the cell surface oligosaccharide structure on these cell types are predictive of phenotypic transition. We have developed, and partially characterized a series of BIOMODULATORS (BM) which delay the onset of display of neoplastic cells. Three classes of BIOMODULATOR have been explored; (1) a large molecular weight natural product (25-35 kDa), PokeWeed Mitogen (PWM); (2) a small molecular weight natural product (500 Da) Cellular Activator and Differentiator (CAD) and a number of natural and synthetic analogs; and (3) an indolizidine alkaloid natural product, Swainsonine (Sw) which has a known cellular target (oligosaccharide biosynthesis). Preliminary data is presented which structurally links some of these BIOMODULATORS in terms of their effective stereochemistry. These BIOMODULATORS, when used before PDL 38, prevent the cell surface oligosaccharide display changes typical of morphological senescence and delay their onset to PDL 100 or more. These BIOMODULATORS also appear to have regulatory effects on the neoplastic cell models. This re-regulation results in increases in generation time and an increase in the ability of these cells to be recognized by cytotoxic lymphocytes. Proton NMR linewidth measurements of the fraction of 'bound' water associated with the cellular surface of treated and untreated cell populations showed induced physical changes in the cell surface related to the use of the BIOMODULATOR and correlated to the oligosaccharide display changes. These data were interpreted as indicating an increase in the organizational level of these cells. The data for normal and neoplastic cell populations are compared and contrasted in an effort to form the basis for an analytical approach to the control and integration of differentiation mechanisms.

Low affinity interaction of peptide-MHC complexes with T cell receptors

The interaction of antigen-specific T cell receptors (TCRs) with their ligands, peptides bound to molecules of the major histocompatibility complex (MHC), is central to most immune responses, yet little is known about its chemical characteristics. The binding to T cells of a labeled monoclonal antibody to the TCR was inhibited by soluble class II MHC heterodimers complexed to different peptides. Inhibition was both peptide- and TCR-specific and of low affinity, with a KD = 4 x 10(-5) to 6 x 10(-5) M, orders of magnitude weaker than comparable antibody-antigen interactions. This finding is consistent with the scanning nature of T cell recognition and suggests that antigen-independent adhesion precedes TCR engagement.

Prevention of xenograft rejection by masking donor HLA class I antigens

Destruction of target cells by cytotoxic T lymphocytes requires the presence of HLA (human lymphocyte antigen) class I antigens on the target cells for adhesion as well as for triggering of the antigen-specific T cell receptor. Rejection of xenogeneic human pancreatic islets and liver was circumvented by masking, before transplantation, donor antigens with F(ab')2 antibody fragments to HLA class I or tissue-specific epitopes. This strategy eliminated the need for recipient immunosuppression and allowed islet xenograft survival beyond 200 days, as demonstrated functionally by C peptide secretion as well as by histology. These in vivo observations are consistent with the importance of donor HLA class I in eliciting graft rejection and have potential applicability to the successful transplantation of other HLA class I-bearing donor tissues.

Specific changes in peripheral blood lymphocyte phenotype from burn patients. Probable origin of the thermal injury-related lymphocytopenia

T-lymphocyte subsets from 27 severely burned patients and 32 controls were analysed using monoclonal antibody immunofluorescent staining and flow cytometry. Compared to normal controls, burn patients showed a remarkable reduction in absolute number of CD3-lymphocytes in the 48 h following injury, which was accounted for by a decrease in both CD4 and CD8 subsets. Activated lymphocytes, as defined by expression of CD25, CD69 and CD71, were significantly increased in burned patients. Additionally, a moderate increase in lymphocytes bearing simultaneously CD4 and CD8 was observed in some burned patients. The expression of CD11c, CD49a and CD54, members of the integrin family of cell surface molecules, was shown to be increased on lymphocytes from thermally injured patients. We conclude that thermal injury produces a profound T-cell lymphopenia with features of extensive T-cell activation, and postulate that depletion of circulating T-cells could be related with the expression of surface adhesion molecules and cell redistribution from blood to the tissues.

Effects of hyperthermia on microtubule organization and cytolytic activity of murine cytotoxic T lymphocytes

When murine cytotoxic T lymphocytes (CTL) are heated at 42 degrees C for 30 min their ability to lyse their target cells (TC) is severely impaired. When the CTL are allowed to recover at 37 degrees C, a partial recovery of cytolytic activity that peaks within 6 h is observed. A dye exclusion assay demonstrated that such a heat shock does not affect the viability of the CTL and direct microscopic observations established that their ability to bind to TC is not impaired. Therefore, the step or steps inhibited by hyperthermia are subsequent to TC recognition and binding. Kupfer et al. ((1983) Proc. Natl. Acad. Sci. USA 80, 7224-7228) demonstrated that upon binding to an appropriate TC, a rapid orientation of the Golgi apparatus and the microtubule organizing center (MTOC) occurred within the CTL so that the two organelles face the TC. This orientation is a prerequisite for efficient TC lysis. We have shown by immunofluorescence and confocal microscopy, using a monoclonal antibody to tubulin and a rabbit autoimmune serum that binds a centriole-associated protein, that the organization of the MTOC-microtubule array is disrupted by hyperthermia. EM suggests that this disorganization of the microtubules may result from an aggregation of the pericentriolar material. The recovery of cytolytic activity is coincident with the reorganization of the microtubules about the MTOC. These findings suggest that the initial inhibitory effect of hyperthermia on CTL function results from the disruption of microtubule organization.

Regulation of LFA-1-mediated T cell adhesion by CD4

Heterotypic adhesion of T lymphocytes to monocytes, B lymphocytes, or other target cells is mainly mediated by LFA-1 and CD2 molecules. Low-affinity binding of resting T cells can be transiently up-regulated by cross-linking of CD3. We have previously found that binding of specific ligands to CD4 can down-regulate adhesion of resting T cells to B cells. We now show that the enhanced adhesiveness of CD4+ T cells induced by CD3 cross-linking using plastic-bound anti-CD3 antibody can also be inhibited by several CD4 ligands. i.e. anti-CD4 antibodies, the gp160 env protein of human immunodeficiency virus, as well as by putative CD4 ligands, i.e. synthetic peptides analogous to the gp160-binding site to CD4 (positions 418-434 and 449-464) and a 12-mer synthetic peptide (DR-12) analogous to positions 35-46 of HLA class II beta subunit and including the highly conserved Arg-Phe-Asp-Ser (RFDS) sequence. After CD3 cross-linking, maximal binding of T cells to HLA class II-positive and -negative B cells was similar, although binding to HLA class II-negative B cells was more prolonged. T cells that were passively induced to up-regulate adhesion by binding of a CD11a-specific antibody NKIL16, known to enhance LFA-1-dependent adhesiveness, were less sensitive to the inhibitory effect of the DR-12 peptide, whereas the inhibitory effects of gp160 were preserved. The kinetics of adhesion of NKIL16-pretreated T cells was not influenced by HLA class II expression at the B cell surface. Together, these results strongly suggest that CD4-HLA class II interaction may down-regulate low-affinity adhesion of resting T cells and, to some extent, high-affinity adhesion of T cells actively induced by CD3 cross-linking but not passively induced by an anti-CD11a antibody.

Activation of LFA-1 through a Ca2(+)-dependent epitope stimulates lymphocyte adhesion

The leukocyte function-associated molecule-1 (LFA-1) plays a key role in cell adhesion processes between cells of the immune system. We investigated the mechanism that may regulate LFA-1-ligand interactions, which result in cell-cell adhesion. To this end we employed an intriguing anti-LFA-1 alpha mAb (NKI-L16), capable of inducing rather than inhibiting cell adhesion. Aggregation induced by NKI-L16 or Fab fragments thereof is not the result of signals transmitted through LFA-1. The antibody was found to recognize a unique Ca2(+)-dependent activation epitope of LFA-1, which is essentially absent on resting lymphocytes, but becomes induced upon in vitro culture. Expression of this epitope correlates well with the capacity of cells to rapidly aggregate upon stimulation by PMA or through the TCR/CD3 complex, indicating that expression of the NKI-L16 epitope is essential for LFA-1 to mediate adhesion. However, expression of the NKI-L16 epitope in itself is not sufficient for cell binding since cloned T lymphocytes express the NKI-L16 epitope constitutively at high levels, but do not aggregate spontaneously. Based on these observations we propose the existence of three distinct forms of LFA-1: (a) an inactive form, which does not, or only partially exposes the NKI-L16 epitope, found on resting cells; (b) an intermediate, NKI-L16+ form, expressed by mature or previously activated cells; and (c) an active (NKI-L16+) form of LFA-1, capable of high affinity ligand binding, obtained after specific triggering of a lymphocyte through the TCR/CD3 complex, by PMA, or by binding of NKI-L16 antibodies.

T cell targeting in cancer therapy

Targeting of immune cells by bispecific antibodies has proven a powerful tool for the investigation of cellular cytotoxicity, lymphocyte activation and induction of cytokine production, as well as to represent an innovative form of immunotherapy for the treatment of cancer. The hallmark of this approach is the use of the specificity of monoclonal antibodies to join target and immune cells by virtue of the dual specificity of bispecific antibodies for the two entities. More precisely the bispecific antibody has two different binding sites, which are capable of recognizing tumor associated antigens on the one hand and lymphocyte activation sites on the other. This process of crosslinking results in the activation of the lymphocyte and triggering of its lytic machinery, as well as lymphokine production. A major advantage of this therapeutic modality is, that use is made of the normal cellular immune defence system and therefore is only associated with minor toxicity. The distinct lymphocyte populations, which can be used for adoptive immunotherapy and the various bispecific antibody preparations, as well as the chimeric immunoglobulin/T cell receptor construction are the major topics of this review.

Allografts of muscle precursor cells persist in the non-tolerized host

Implantation of normal muscle precursor cells into myopathic fibres to alleviate recessively inherited diseases of skeletal muscle has received much attention since the discovery of a defective or deficient gene coding for the protein dystrophin in the Duchenne and Becker forms of muscular dystrophy. Therapeutic allografting of cells would require some means of preventing their immune rejection. Here we have allografted muscle into the non-tolerant and non-immunosuppressed murine host. Precursor cells introduced in the form of a single cell suspension survive for prolonged periods post-implantation. Allografts of minced muscle often failed to survive, even though host and donor were compatible at the major histocompatibility locus. Differences at minor loci may well have contributed to such rejection. Where allografted tissue was rejected, there was a decrease in the amount of surviving host muscle at the graft site, an important observation in terms of the therapeutic implantation of cells.

Functional characteristics of the intercellular adhesion molecule-1 (CD54) expressed on cytotoxic human blood lymphocytes

We have shown that intercellular adhesion molecule-1 (ICAM-1) (CD54) positive cells are mainly responsible for the natural cytotoxic function of human blood lymphocytes. The evidences were the inhibition of cytotoxicity by anti-ICAM-1 (LB-2) monoclonal antibodies (mAb) and the loss of lytic activity after removal of the ICAM-1+ cells. In addition, the cytotoxic potential of the separated ICAM-1- lymphocyte population after activation appeared in parallel with the expression of this molecule. The ICAM-1+ lymphocytes lysed both LFA-1 (CD11a/CD18 or Leu-CAMa) positive and negative cell lines, and pretreatment of the effectors with the LB-2 mAb also inhibited the lysis of LFA-1- targets. The results point to a yet unrecognized role of ICAM-1 on the lymphocytes. Kinetics experiments suggested that pretreatment of lymphocytes with alpha-ICAM-1 (LB-2) mAb did not inhibit the promptly established lytic interactions but influenced later events, recycling and/or recruitment of effectors. It is possible that the cytotoxic potential is regulated by contacts between the members of the lymphocyte population and that these events occur via their ICAM-1 and LFA-1. Exposure of lymphocytes to NK-sensitive targets for 16 hr elevated their cytotoxic potential. The function of activated lymphocytes was not inhibited by the LB-2 mAb.

Two-way signalling through the LFA-1 lymphocyte adhesion receptor

T lymphocyte recognition of foreign antigens and migration throughout the body require the regulated adhesion of lymphocytes to diverse types of cells and to the extracellular matrix. The lymphocyte adhesion 'receptor' LFA-1, a member of the integrin family, interacts with ICAM-1 and other counter-receptors to mediate adhesion. The LFA-1/ICAM-1 interaction is regulated by signals transmitted from the cytoplasm to the extracellular space. Conversely, LFA-1 transmits signals from the extracellular space to the cytoplasm to regulate T lymphocyte activation. The observed properties of LFA-1 and related adhesion 'receptors' are incorporated into a general model for adhesion during immune surveillance and recognition of foreign antigens.

T-cell receptor-negative natural killer cells display antigen-specific cytotoxicity for microvascular endothelial cells

Based upon prior demonstrations that human microvascular endothelial cells (ECs) could serve as natural killer (NK) cell targets, we established NK cell lines and clones by repeated stimulation of highly purified CD16-positive, CD3/T-cell receptor (Ti)-negative cells with allogeneic ECs. After 3 weeks in culture these lymphoid cells, which neither expressed surface CD3/Ti molecules nor rearranged Ti beta- or gamma-chain genes and which lysed K562 human erythroleukemia cells, displayed specific cytotoxicity for the stimulating ECs. Furthermore, freshly isolated NK cells bound and then removed from each of several allogeneic EC lines displayed selective cytotoxicity for the adsorbing EC line. These results provide evidence for alloantigen-specific recognition of microvascular ECs by NK cells that appears to be determined, at least in part, at the level of adherence. We discuss the implications of these findings with respect to the rejection of vascularized organ allografts.

Adhesion receptors of the immune system

The adhesive interactions of cells with other cells and with the extracellular matrix are crucial to all developmental processes, but have a central role in the functions of the immune system throughout life. Three families of cell-surface molecules regulate the migration of lymphocytes and the interactions of activated cells during immune responses.