The role of monocyte lymphocyte function-associated antigen 1 (LFA-1) in accessory cell function

Cafeteria diet-induced obesity remodels immune response in acute Trypanosoma cruzi infection

BACKGROUND

Obesity is a global problem associated with several conditions, including hypertension, diabetes, arthritis and cardiovascular diseases. With the increase in the prevalence of obesity in recent years, mostly in developing countries, it is important to study its impact on various diseases, including infectious illnesses, such as Chagas disease, caused by the protozoan Trypanosoma cruzi. Considering that a diet rich in salt, sugar, and fat is associated with obesity, this study aimed to evaluate the influence of cafeteria diet (CAF)-induced obesity on immune responses in T. cruzi-infected rats.

METHODS

Male Wistar Hannover rats were provided with water and food ad libitum (chow group). The CAF-fed groups received a normal rodent diet or CAF. The animals were intraperitoneally infected with 105 trypomastigote forms of the Y strain of T. cruzi present in the whole blood from a previously infected mouse.

RESULTS

CAF-fed rats showed a significant increase in visceral adipose tissue weight compared to chow-fed rats. A significant reduction in CD3+ CD4+ helper splenic T cells was observed in obese-infected rats compared to non-obese-infected rats, as well as CD11b and macrophages. In addition, macrophages from obese animals displayed reduced RT1b levels compared to those from control animals. Moreover, INF-γ, an important factor in macrophage activation, was reduced in obese-infected rats compared with their counterparts.

CONCLUSIONS

These results indicate that a CAF can impair the cell-mediated immune response against T. cruzi.

Immunological Insights into Cigarette Smoking-Induced Cardiovascular Disease Risk

Smoking is one of the most prominent addictions of the modern world, and one of the leading preventable causes of death worldwide. Although the number of tobacco smokers is believed to be at a historic low, electronic cigarette use has been on a dramatic rise over the past decades. Used as a replacement for cigarette smoking, electronic cigarettes were thought to reduce the negative effects of burning tobacco. Nonetheless, the delivery of nicotine by electronic cigarettes, the most prominent component of cigarette smoke (CS) is still delivering the same negative outcomes, albeit to a lesser extent than CS. Smoking has been shown to affect both the structural and functional aspects of major organs, including the lungs and vasculature. Although the deleterious effects of smoking on these organs individually is well-known, it is likely that the adverse effects of smoking on these organs will have long-lasting effects on the cardiovascular system. In addition, smoking has been shown to play an independent role in the homeostasis of the immune system, leading to major sequela. Both the adaptive and the innate immune system have been explored regarding CS and have been demonstrated to be altered in a way that promotes inflammatory signals, leading to an increase in autoimmune diseases, inflammatory diseases, and cancer. Although the mechanism of action of CS has not been fully understood, disease pathways have been explored in both branches of the immune system. The pathophysiologically altered immune system during smoking and its correlation with cardiovascular diseases is not fully understood. Here we highlight some of the important pathological mechanisms that involve cigarette smoking and its many components on cardiovascular disease and the immune systems in order to have a better understanding of the mechanisms at play.

Efalizumab binding to the LFA-1 alphaL I domain blocks ICAM-1 binding via steric hindrance

Lymphocyte function-associated antigen 1 (LFA-1) plays important roles in immune cell adhesion, trafficking, and activation and is a therapeutic target for the treatment of multiple autoimmune diseases. Efalizumab is one of the most efficacious antibody drugs for treating psoriasis, a very common skin disease, through inhibition of the binding of LFA-1 to the ligand intercellular adhesion molecule 1 (ICAM-1). We report here the crystal structures of the Efalizumab Fab alone and in complex with the LFA-1 alpha(L) I domain, which reveal the molecular mechanism of inhibition of LFA-1 by Efalizumab. The Fab binds with an epitope on the inserted (I) domain that is distinct from the ligand-binding site. Efalizumab binding blocks the binding of LFA-1 to ICAM-1 via steric hindrance between its light chain and ICAM-1 domain 2 and thus inhibits the activities of LFA-1. These results have important implications for the development of improved antibodies and new therapeutic strategies for the treatment of autoimmune diseases.

Identification and characterization of a human monoclonal antagonistic antibody AL-57 that preferentially binds the high-affinity form of lymphocyte function-associated antigen-1

LFA-1 (alpha(L)beta(2)) mediates cell-cell and cell-extracellular matrix adhesions essential for immune and inflammatory responses. One critical mechanism regulating LFA-1 activity is the conformational change of the ligand-binding alpha(L) I domain from low-affinity (LA), closed form, to the high-affinity (HA), open form. Most known integrin antagonists bind both forms. Antagonists specific for the HA alpha(L) I domain have not been described. Here, we report the identification and characterization of a human antibody AL-57, which binds to the alpha(L) I domain in a HA but not LA conformation. AL-57 was discovered by selection from a human Fab-displaying library using a locked-open HA I domain as target. AL-57 Fab-phage bound HA I domain-expressing K562 cells (HA cells) in a Mg(2+)-dependent manner. AL-57 IgG also bound HA cells and PBMCs, activated by Mg(2+)/EGTA, PMA, or DTT. The binding profile of AL-57 IgG on PBMCs was the same as that of ICAM-1, the main ligand of LFA-1. In contrast, an anti-alpha(L) murine mAb MHM24 did not distinguish between the HA and LA forms. Moreover, AL-57 IgG blocked ICAM-1 binding to HA cells with a potency greater than MHM24. It also inhibited ICAM-1 binding to PBMCs, blocked adhesion of HA cells to keratinocytes, and inhibited PHA-induced lymphocyte proliferation with potencies comparable with MHM24. These results indicate that specifically targeting the HA I domain is sufficient to inhibit LFA-1-mediated, adhesive functions. AL-57 represents a therapeutic candidate for treatment of inflammatory and autoimmune diseases.

Transactivation of the ICAM-1 gene by CD30 in Hodgkin's lymphoma

The ICAM-1/LFA-1 complex mediates cell-cell interaction. ICAM-1 is overexpressed in Hodgkin/Reed-Sternberg (H/RS) cells, and serum levels of its soluble form are higher in Hodgkin's lymphoma (HL) patients than in controls. There are no data, however, regarding the regulation of expression of ICAM-1 in H/RS cells. CD30 was identified in H/RS cells of HL and has attracted much interest as a molecular marker of HL. To analyze ICAM-1 expression in H/RS cells, we examined the expression of ICAM-1, LFA-1, CD30 and CD30L in HL-derived cell lines. All cell lines expressed ICAM-1 and CD30, but not LFA-1 or CD30L. CD30 induced ICAM-1 expression. Analysis of the ICAM-1 promoter showed the importance of NF-kappaB binding site for CD30-induced ICAM-1 gene expression. Coexpression of IkappaB, IKK, NIK and TRAF dominant-negative constructs with CD30 inhibited CD30-induced activation of ICAM-1 promoter, suggesting that CD30 induces ICAM-1 via NF-kappaB signalling. The ICAM-1 promoter was activated by the C-terminal region of CD30, which activated NF-kappaB signalling. A decoy CD30 lacking the cytoplasmic region inhibited ICAM-1 promoter activity in HL cell lines. Thus, in H/RS cells, ligand-independent activation of CD30 signalling activates NF-kappaB and this leads to constitutive ICAM-1 expression, suggesting a link between 2 well known phenotypic characteristics of HL, CD30 and ICAM-1 overexpression.

Deficiency of CD11b or CD11d Results in Reduced Staphylococcal Enterotoxin-Induced T Cell Response and T Cell Phenotypic Changes

The beta(2) integrin CD11a is involved in T cell-APC interactions, but the roles of CD11b, CD11c, and CD11d in such interactions have not been examined. To evaluate the roles of each CD11/CD18 integrin in T cell-APC interactions, we tested the ability of splenocytes of CD11-knockout (KO) mice to respond to staphylococcal enterotoxins (SEs), a commonly used superantigen. The defect in T cell proliferation with SEA was more severe in splenocytes from mice deficient in CD18, CD11b, or CD11d than in CD11a-deficient splenocytes, with a normal response in CD11c-deficient splenocytes. Mixing experiments showed that the defect of both CD11b-KO and CD11d-KO splenocytes was, unexpectedly, in T cells rather than in APC. Cytometric analysis failed to detect CD11b or CD11d on resting or activated T cells or on thymocytes of wild-type adult mice, nor did Abs directed to these integrins block responses in culture, suggesting that T cells educated in CD11b-KO or CD11d-KO mice were phenotypically altered. Consistent with this hypothesis, T cells from CD11b-KO and CD11d-KO splenocytes exhibited reduced intensity of CD3 and CD28 expression and decreased ratios of CD4/CD8 cells, and CD4(+) T cells were reduced among CD11b-KO and CD11d-KO thymocytes. CD11b and CD11d were coexpressed on a subset of early wild-type fetal thymocytes. We postulate that transient thymocyte expression of both CD11b and CD11d is nonredundantly required for normal thymocyte and T cell development, leading to phenotypic changes in T cells that result in the reduced response to SE stimulation.

Modulating T cell responses for the treatment of psoriasis: a focus on efalizumab

An improved understanding regarding the pathophysiology of psoriasis, coupled with advances in molecular research, has prompted the development of targeted biologic treatments for patients with plaque psoriasis. T lymphocytes play an important role in initiating the immune system and the inflammatory responses that result in the development and maintenance of psoriatic plaques. Efalizumab (anti-CD11a, Raptiva; Genentech, Inc.) is a mAb that targets the T cell adhesion molecule, leukocyte function-associated antigen-1 (LFA-1). By binding to CD11a - the alpha-subunit of LFA-1 - LFA-1 is prevented from binding with its ligand, intercellular adhesion molecule-1 (ICAM-1). This inhibits various T cell processes believed to be important in the pathogenesis of psoriasis, including T cell activation, T cell adhesion to endothelial cells and T cell migration. Clinical trials demonstrate that efalizumab, given subcutaneously once-weekly, provides clinical benefit, including improved quality of life, in patients with moderate-to-severe plaque psoriasis. Efalizumab is associated with an early onset of action, with improvement noted as early as 14 days. Studies with extended treatment suggest that continuing efalizumab therapy is more beneficial in maintaining and improving responses. Relapse of psoriasis is usually seen within 60 - 70 days after discontinuation of therapy, and rebound in approximately 5% of patients (i.e., flare to > 125% of baseline) is noted. Efalizumab is associated with acute adverse events during the first and second injections, which decrease in incidence with each subsequent injection. Data indicate that efalizumab can be safely administered for extended periods of time. Given the efficacy, early onset of clinical benefit, the safety profile and the convenience of once-weekly subcutaneous home dosing, efalizumab offers an interesting new therapeutic option for the treatment of psoriasis and the potential for improved and potentially safer long-term, continuous 'maintenance' therapy.

Regulation of lymphocyte clustering by CD30-mediated ICAM-1 up-regulation

CD30 is expressed transiently on activated B and T lymphocytes and constitutively on several B- and T cell lymphomas. CD30 functions include participation in negative selection of thymocytes, costimulation of activated T cells, isotype switching of B cells, and regulation of the effector activity of cytotoxic lymphocytes. Although CD30 is not a marker for T helper 2 (TH2) cells, it may participate in the polarization of TH1 and TH2 cells. The pleiotropic functions of CD30 are initiated by interaction of CD30-expressing cells with other immune competent cells expressing CD30-L and providing the signals for modulation of effector cell activity. Here, we report that CD30 signals generated by anti-CD30 on activated, normal murine T cells strongly up-regulate the expression of intercellular adhesion molecule 1 (ICAM-1, CD54), and to a lesser extent, ICAM-2 (CD102). CD30 signals moreover delay the subsequent decline of ICAM expression. CD30 cross-linking did not alter the expression of CD11a/CD18 (LFA-1), the counter receptor for ICAM abundant on T cells. CD30-mediated ICAM-1 up-regulation is independent of cytokine secretion and appears to be transmitted directly through NF-kappaB activation. CD30-mediated up-regulation of ICAM-1 expression led to a significant increase in cluster formation of lymph node cells. Increased lymphocyte self-aggregation mediated by CD30 may set the stage for fraternal signaling to modulate lymphocyte function.

The complement receptor 3, CR3 (CD11b/CD18), on T lymphocytes: activation-dependent up-regulation and regulatory function

The complement receptor 3 (CR3; CD11b/CD18) is present exclusively on leukocytes, particularly on NK cells, monocytes and polymorphonuclear neutrophils. Approximately 10% of peripheral T lymphocytes and, as we found now mainly CD8(+) cells, expressed CD11b. Upon stimulation, however, expression of CD11b was up-regulated also on CD4(+) cells. Stimulation of T cells either by cross-linked anti-CD3 and IL-2 or by mononuclear cells and mitogen yielded up to 28% CD11b(+) T cells. The majority of CD11b(+) T cells also expressed CD56. T cell lines established from healthy donors were also found to express CR3. When restimulated up to 90% of cells became positive for CD11b making those cells an ideal tool for studying the functional role of CD11b. Antibodies to CD11b and bona fide ligands for the complement receptor inhibited the anti-CD3-induced T cell proliferation and as well as IL-2 release. In contrast, proliferation of a CD11b(-) T cell line was not inhibited. Taken together, our data indicate an activation-dependent expression of the complement receptor on T cells and suggest a regulatory function.

Induction of adhesion molecules on human schwann cells by proinflammatory cytokines, an immunofluorescence study

The presence of cytokines in the peripheral nerve was positively correlated to the induction and progression of inflammation during experimental allergic neuritis (EAN) and Guillain Barré syndrome (GBS). We investigated the induction of adhesion molecules such as L-selectin, E-selectin, ICAM-1, VCAM-1 and Mac-1 on Schwann cells by proinflammatory cytokines. Cultured human Schwann cells from normal adult, fetal and diabetic nerves were studied by immunofluorescence at basal condition and after stimulation with cytokines for 6, 24, 48 and 96 h. Incubation of human Schwann cells with TNFalpha, IFNgamma and IL-1beta induces the expression of ICAM-1 starting at 6 h and reaching a peak at 24 h on more than 90% of cells. VCAM-1 expression was induced after 6 h of treatment with TNFalpha and IL-1beta on almost 100% of Schwann cells. Surprisingly, stimulation with TNFalpha, IFNgamma and IL-1beta also induced the expression of L-selectin on fetal and diabetic Schwann cells, but not on normal adult cells. E-selectin, an adhesion molecule classically upregulated during inflammation, as well as Mac-1, a ligand for ICAM-1, were not expressed on human Schwann cells at basal condition or after treatment with cytokines. No ICAM-1, VCAM-1 and L-selectin expression was found on unstimulated Schwann cells. Our results suggest that upregulation of adhesion molecules on Schwann cells may have a role in the pathogenesis of inflammation in the peripheral nerve.

In situ analysis of adhesion molecule expression in kidneys infected with murine malaria

The expression of intercellular adhesion molecule-1 (ICAM-1), the ligand leucocyte function antigen-1 (LFA-1, CD11a), and complement receptor type 3 (CR3, or Mac-1, CD11b) has been studied in murine kidneys acutely infected with the fatal malaria parasite Plasmodium berghei ANKA. Thirty-six kidney sections from five groups of C57BL/6J mice on day 5, 10, 15, and 20 post-infection, and normal controls, were stained with monoclonal antibodies against ICAM-1, LFA-1, and Mac-1. There was markedly enhanced expression of ICAM-1 in the glomerular mesangium and the endothelium of blood vessels from day 10 post-infection. ICAM-1 was also found in the proximal tubular epithelial cells in an apical location, with a linear pattern. In addition, the glomeruli showed positive staining for LFA-1 and Mac-1 on day 10 post-infection, mainly in the infiltrating inflammatory cells. Mesangial cells and inflammatory cells in the cortical tubulointerstitium showed positive staining for ICAM-1, LFA-1, and Mac-1 at the later stages of infection. There were strong correlations between ICAM-1 expression on endothelial cells of glomerular/peritubular capillaries with inflammatory cells positive for LFA-1 and Mac-1, which correlated with proteinuria. These findings show that several adhesion molecules are up-regulated in murine malaria-associated nephritis. The expression of ICAM-1 on endothelial cells correlated with the severity of inflammatory responses, indicating the relationship between the expression of adhesion molecules and cell-mediated immune renal injury. It is suggested that adhesion molecules play an important role in the pathogenesis of murine nephritis. Better knowledge of the function of these molecules in malaria infection may open new approaches to antimalarial therapy.

Antigen-specific immune responses in cattle with inherited beta2-integrin deficiency

The significance of beta2-integrins for the generation of antigen-specific immune responses in vivo was studied employing the bovine model of beta2-integrin deficiency. To that end four cattle with bovine leukocyte adhesion deficiency (BLAD) and healthy age-matched controls were immunized with tetanus toxoid (TT) and rabies virus (RV) vaccines three times in monthly intervals. In addition, two animals with BLAD and three controls received a fourth vaccination 8 months after the start of the study. Proliferative responses of peripheral blood mononuclear cells (PBMC) to the antigens TT and RV as well as specific serum immunoglobulin G (IgG) titers were determined in intervals for up to 10 months after primary vaccination. Proliferative responses of PBMC to TT and RV were substantially lower in cattle with BLAD than in controls, although PBMC from cattle with BLAD were shown to have the capacity to proliferate in the response to the mitogen concanavalin A. Occurrence of antigen-specific IgG titers was delayed and they were considerably lower in cattle with BLAD compared to controls. Finally, treatment of TT- and RV-stimulated PBMC from an immunized control with different concentrations of the anti-CD18 monoclonal antibody R15.7 resulted in a dose-dependent inhibition of lymphocyte proliferation to almost 100%. The results of the present study show that beta2-integrin deficiency leads to delayedand severely impaired immune responsiveness in vivo. The observations that antibody production, although considerably delayed and impaired, does occur and that apparently class-switching takes place in BLAD indicate T-cell reactivity in vivo.

Detection of human topoisomerase II alpha in cell lines and tissues: characterization of five novel monoclonal antibodies

We report five novel monoclonal antibodies (Ki-S1, Ki-S4, Ki-S6, Ki-S7, and Ki-S8) reactive with a proliferation-related nuclear antigen. In immunoprecipitation and Western blot experiments using crude nuclear extracts, they recognized a protein of 170 kD that, after proteolytic digestion of the immunoprecipitate and sequencing of the resulting peptides, was identified as the alpha-isoform of human topoisomerase II. This was confirmed by testing the antibodies on a highly purified enzyme preparation. Crossreactivity with topoisomerase II beta was ruled out by testing the antibodies on crude extracts from yeast cells expressing the beta-isoform exclusively. The antibodies bind the antigen with different affinities and at different epitopes, apparently located within the carboxyl third of the enzyme. All five antibodies are suitable for archival material after adequate antigen retrieval, thereby enabling retrospective studies. This report illustrates the tissue and subcellular distribution of the antigen through the cell cycle by immunohistochemistry and confocal fluorescence microscopy. The antibodies will be useful tools in further analysis of morphological and functional aspects of topoisomerase II and may serve diagnostic purposes, as well as providing prognostic information in tumor pathology.

Expression of gamma delta T cells and adhesion molecules in endometriotic tissue in patients with endometriosis and adenomyosis

PROBLEM

Are T cell subsets including gamma delta T cells. HLA antigens or adhesion molecules, expressed in eutopic and ectopic endometria in patients with endometriosis and adenomyosis?

METHODS

Subjects consisted of 23 patients with adenomyosis and 21 patients with endometriosis. Controls consisted of 15 patients with adenomyoma and 42 infertile women without habitual abortion and autoimmune diseases. Staining of the glandular cells in eutopic and ectopic endometria or T lymphocyte subsets or macrophages in the stroma were analyzed immunohistochemically to localize the expression of the antigens.

RESULTS

Immunohistochemical analysis revealed significantly increased expression of the antigens, particularly of the number of gamma delta T cells in the stroma and adhesion molecules and HLA antigens on the glandular cells in eutopic and ectopic endometria, compared with materials from patients with adenomyoma and infertile patients.

CONCLUSION

It is likely that three distinct pathways of cell-cell interactions are activated in patients with endometriosis or adenomyosis.

Effect of danazol on the immunocompetent cells in the eutopic endometrium in patients with endometriosis: a multicenter cooperative study

OBJECTIVE

To assess the effects of danazol on immunocompetent cells, human leukocyte antigen (HLA) expression, and adhesion molecules in the eutopic endometrium of patients with endometriosis.

DESIGN

Antigens were localized immunohistochemically in the endometria, before treatment and during treatment (2 months later).

PARTICIPANTS

Ten patients with laparoscopically proven endometriosis who consented to participate in this study were treated with 400 mg/d of danazol for 4 months. Forty-two infertile patients without endometriosis or adenomyosis served as controls.

RESULTS

Immunohistochemical analysis revealed significantly increased expression of the T cell subsets, macrophages, adhesion molecules, and HLA antigens in eutopic endometrium in patients with endometriosis compared with the infertile group. Treatment with danazol reduced the number of cells in T cell subsets, adhesion molecules, or HLA antigen expression, especially of gamma delta T cells, to 39.5% of the pretreatment value in patients with endometriosis.

CONCLUSIONS

Danazol had an immunomodulatory effect on the autoimmune response in endometrium associated with endometriosis.

In vitro cell aggregation and cell adhesion molecules in Crohn's disease

BACKGROUND

Lack of a suitable model has hindered efforts to understand inflammation and granuloma formation in Crohn's disease.

METHODS

Granulomalike aggregates of circulating mononuclear cells are produced in vitro by cultures of cells with polyacrylamide beads. To identify features of in vitro aggregates, which are similar to tissue granulomas of Crohn's disease, the gross morphology and immunohistological appearance of the aggregates produced with peripheral blood mononuclear cells from patients with Crohn's disease were analyzed, and the size of in vitro aggregates was correlated with clinical activity of the disease. Blocking antibodies were used to evaluate the role of cell-adhesion molecules in the formation of in vitro aggregates.

RESULTS

The size of in vitro aggregates correlates very significantly with clinical activity (P < 0.001). In active Crohn's disease, in vitro aggregates show immunohistological features of hypersensitivity type granulomas. Blocking antibodies against leukocyte function associated antigen LFA-2 (CD2), LFA-3 (CD58), and Mac-1 (CD11b/CD18) inhibit in vitro aggregate formation.

CONCLUSION

In vitro aggregates model in vivo granulomas in size and organization. Cell adhesion molecules like CD2, CD58, and CD11b/CD18 may be involved in granuloma-formation of Crohn's disease.

Increased CD11/CD18 expression on peripheral blood leucocytes of patients with sarcoidosis

Sarcoidosis is a multisystem disease of unknown etiology characterized by non-caseating granulomata, formed mainly from macrophages surrounded by lymphocytes and plasma cells. Using a novel method for the preparation of blood leucocytes for flow cytometry, we report increased expression of LeuCAMs (CD11/CD18) on peripheral blood leucocytes of 11 Caucasian and 10 Afro-Caribbean patients with sarcoidosis compared with age-, sex- and race-matched controls. Whilst the percentages of the cells expressing CD11/CD18 were no different, the density, expressed as mean fluorescence intensity (MFI), was greater for all leucocytes in sarcoids than in normal individuals. The expression of intercellular adhesion molecule-1 (ICAM-1), a ligand for LFA-1 which is expressed on all leucocytes, was not significantly different from normal, whereas HLA-DR was expressed more intensely on sarcoid monocytes (P less than 0.01) and blood lymphocytes (P less than 0.005) than control cells. Our findings are consistent with leucocyte activation although we were unable to confirm reports of elevated tumour necrosis factor-alpha (TNF-alpha) in the patients' plasma using an ELISA. Increased expression of adhesion molecules on peripheral blood leucocytes may play a role in the cellular extravasation, aggregation, and granuloma formation seen in sarcoidosis.

Age-related changes in LFA-1 expression, cell adhesion, and PHA-induced proliferation by lymphocytes from senescence-accelerated mouse (SAM)-P/8 and SAM-R/1 substrains

Accelerated senescence-prone mice of the SAM-P/8jf series were compared with senescence-resistant SAM-R/1 controls in terms of age-related changes in phytohemagglutinin (PHA) proliferative responses and lymphocyte function-associated antigen-1 (LFA-1) utilization by non-adherent splenocytes. Advancing age was associated with a reduction in cell proliferative responses to PHA in both substrains, although the rate of decline was significantly more rapid in the senescence-prone animals. Conversely, in both substrains there was a progressive age-related increase in the proportion of splenocytes expressing high levels of LFA-1, and a parallel increase in the degree of LFA-1-dependent cell aggregation induced by phorbol ester. Age-matched SAM-P/8jf and SAM-R/1 mice did not differ in terms of LFA-1 expression or LFA-1-dependent cell aggregation. Two-color cytofluorometric analysis demonstrated the enhanced expression of LFA-1 expression by cells bearing the Pgp-1hi phenotype characteristic of memory lymphocytes. These results suggest that age-associated changes in lymphocyte adhesion are attributable to alterations in the relative numbers of memory cells expressing high levels of LFA-1, but are unlikely to contribute to the reduced proliferative response to mitogen in aged mice.

Accessory function of human mononuclear phagocytes for lymphocyte responses to the superantigen staphylococcal enterotoxin B

The role of the cytokines IL-1 alpha, IL-1 beta, and IL-6 and the cell adhesion molecules ICAM-1, LFA-1 (alpha and beta), and Mac-1 as accessory molecules for stimulation of T cells by the superantigen staphylococcal enterotoxin B (SEB) was examined. Both blood monocytes and alveolar macrophages were used as accessory cells because these cells differ in patterns of cytokine expression and thus potentially in accessory cell function for superantigens. The blastogenic response of highly purified T cells to SEB was reconstituted with either monocytes or alveolar macrophages. IL-1 secretion was increased comparably in monocytes and alveolar macrophages by SEB, but IL-6 was not stimulated by SEB. IL-1 alpha plus IL-1 beta reconstituted the response of T cells to SEB but required the addition of accessory cells. The cell adhesion molecules ICAM-1 and LFA-1 but not Mac-1 also functioned as accessory molecules for SEB-induced cluster formation and lymphocyte blastogenesis. Thus, not only must this superantigen bind to Class II MHC on accessory cells as is well known, but also SEB requires at least certain cytokines (IL-1 alpha and IL-1 beta) produced by accessory cells and cell adhesion molecules (ICAM-1 and LFA-1) for activation of T lymphocytes.

Interaction of leukocyte integrins with ligand is necessary but not sufficient for function

The leukocyte integrins (CD11/CD18 or beta 2-type integrins) are expressed exclusively on leukocytes and participate in many adhesion-dependent functions (Arnaout, M.A. 1990. Blood. 75:1037-1050; Springer, T. A. 1990. Nature. (Lond.) 346:425-434; Dustin, M. L., and T. S. Springer. 1991. Annu. Rev. Immunol. 9:27-66). The avidity of leukocyte integrin binding to their ligands or counter-receptors is dependent upon response to intracellular signals (Wright, S. D., and B. C. Meyer. 1986. J. Immunol. 136:1759-1764; Dustin, M. A., and T. S. Springer. 1989. Nature (Lond.). 341:619-624). We have investigated the effects of a novel mAb (mAb 24) which defines a leukocyte integrin alpha subunit epitope that is Mg(2+)-dependent and may be used as a "reporter" of the activation state of these receptors (Dransfield, I., and N. Hogg. 1989. EMBO (Eur. Mol. Biol. Organ) J. 8:3759-3765; Dransfield, I., A.-M. Buckle, and N. Hogg. 1990. Immunol. Rev. 114:29-44; Dransfield, I., C. Cabañas, A. Craig, and N. Hogg. 1992. J. Cell Biol.) Data is presented to show that this mAb inhibits monocyte-dependent, antigen-specific T cell proliferation and IL-2-activated natural killer cell assays which are both dependent on lymphocyte function-associated antigen-1 (LFA-1), and complement receptor type 3 (CR3)-mediated neutrophil chemotaxis to f-Met-Leu-Phe. This inhibitory effect is not caused by the prevention of receptor/ligand binding because LFA-1/ICAM-1, LFA-1/ICAM-2,3 and CR3/iC3b interactions are, under activating conditions, promoted rather than blocked by mAb 24. As it does not interfere with mitogen-stimulated T cell proliferation, it is unlikely that mAb 24 transduces a "negative" or antiproliferative signal to the T cells to which it is bound. Using a model system of transient activation of LFA-1, we have found that mAb 24 prevents "deadhesion" of receptor/ligand pairs, possibly locking leukocyte integrins in an "active" conformation. It is speculated that inhibition of leukocyte integrin function by this mAb reflects the necessity for dynamic leukocyte integrin/ligand interactions.

A unique CD44 monoclonal antibody identifies a new T cell activation pathway

We have identified a new T cell activation pathway mediated by the lymphocyte homing receptor/CD44 molecule, 8B2.5, a local monoclonal antibody (mAb), which recognizes two glycoproteins of 85 and 220 kDa with wide tissue distribution, is shown by sequential immunoprecipitations and competitive antibody-binding inhibition experiments with several CD44 reference mAb to recognize the CD44 molecule. The 8B2.5 mAb, but not reference CD44 mAb, is able to induce resting peripheral blood lymphocytes to proliferate in the presence of phorbol esters. This proliferation is monocyte dependent but Fc independent and results from 8B2.5 mAb binding to CD44 molecules both expressed by both T cells and monocytes. In the absence of monocytes, proliferation can be restored by solid-phase 8B2.5 mAb, or, to a lesser extent, by adding interleukin 2. Although CD3 and CD44 surface molecules are found physically independent, T cell activation via the CD44 pathway is inhibited by CD3 modulation. In addition to the direct role of CD44 molecules in T cell proliferation, CD44 mAb can up- or- down-regulate the CD3 and CD28 pathways, depending on the presence of monocytes. These results suggest that T cell and monocyte binding to high endothelial venule or extracellular matrix proteins could further promote clonal expansion of resting T cells migrating in certain specific anatomic sites.

Expression of intercellular adhesion molecule 1 (ICAM-1) in Alzheimer's disease

In this study, 13 clinically and pathologically diagnosed cases of Alzheimer's disease were analyzed for the presence of intercellular adhesion molecule 1 (ICAM-1), ICAM-2, lymphocyte function associated antigen-1 (LFA-1), HLA-DR, LN-1, and LN-2. ICAM-1 was observed primarily on neuritic plaques and cerebrovascular endothelium. ICAM-1 was also shown to be present in brain tissue derived from 14 normal cases; however, the degree of immunoreactivity was quantitatively less compared to Alzheimer cases and was largely restricted to cerebrovascular endothelium. LFA-1 was shown to be present on microglial cells and leukocytes. Consistent with the findings of previous reports, HLA-DR was found to be expressed on microglial cells. In this study we failed to demonstrate dual immunolocalization for ICAM-1 and LFA-1, ICAM-1 and HLA-DR, or ICAM-1 and LN-2. As microglial cells express both HLA-DR and LFA-1, they may serve to mediate antigen presentation functions by interacting with lymphocyte ICAM-1. Alternately, the expression of these immune-associated glycoproteins on glial cells may be epiphenomenal occurring secondary to some aspect of the disease process. Finally, the presence of ICAM-1 within neuritic plaques raises the question as to whether adhesion may play some role in the process of neurite outgrowth and neurodegeneration.

Increased expression of leukocyte function associated antigen-1 (LFA-1) and intercellular adhesion molecule-1 (ICAM-1) by alveolar macrophages of patients with pulmonary sarcoidosis

Leukocyte function associated antigen-1 (LFA-1) and its ligand intercellular adhesion molecule-1 (ICAM-1) are cell adhesion molecules that play an important role in the capacity of monoculear phagocytes (MPs) to present antigens to T lymphocytes. Since in pulmonary sarcoidosis (PS) this capacity is increased at sites of disease activity, we studied the expression of LFA-1 and ICAM-1 on peripheral blood monocytes (BMs) and alveolar macrophages (AM) obtained by bronchoalveolar lavage (BAL) from normal subjects (n = 7) and patients with PS (n = 14). To accomplish this, immunocytochemical stainings were made on cytocentrifuge preparations using anti-LFA-1 (anti-CD 11a) and anti-ICAM-1 (anti-CD 54) monoclonal antibodies (MoAbs). Normal and sarcoid BMs displayed a high percentage of positivity with both MoAbs with no difference between study groups (LFA-1: control BM 87.8 +/- 8.8 percent; sarcoid BM 84.7 +/- 9.5 percent; ICAM-1: control BM 80.8 +/- 10 percent; sarcoid BM 88.0 +/- 4.2 percent; p = NS for all comparisons). In both groups the percentage of cells expressing LFA-1 and ICAM-1 molecules among AMs was lower than among autologous BMs (LFA-1: control AM 46.5 +/- 13.2 percent, p less than 0.001 vs control BM; sarcoid AM 64.2 +/- 15.9; p less than 0.001 vs sarcoid BM) (ICAM-1: control AM 42.7 +/- 8.5 percent, p less than 0.001 vs control BM; sarcoid AM 72.1 +/- 10.6, p less than 0.001 vs sarcoid BM). AMs from patients with PS showed a higher degree of positivity for LFA-1 and ICAM-1 than normal AMs (p less than 0.02 and p less than 0.001, respectively). The positivity for LFA-1 and ICAM-1 molecules on sarcoid AMs was not correlated with the positivity for two different BM-associated markers (ie, the CD 11b and the CD 14 molecules) and was not correlated with the percentage of T lymphocytes in BAL, selected as a marker of the intensity of the alveolitis. These results suggest that the increased ability of sarcoid AMs to induce the proliferation of T lymphocytes may be related, at least in part, to the increased expression of LFA-1 and ICAM-1 molecules on their surfaces.

Parasite-accessory cell interactions in theileriosis. Antigen presentation by Theileria annulata-infected macrophages and production of continuously growing antigen-presenting cell lines

Theileria annulata, a protozoan parasite of cattle, infects major histocompatibility complex (MHC) class II+ cells, particularly macrophages, and transforms them into continuously growing cell lines. We examined the effects of parasitism by T. annulata on antigen-presenting cell function. T. annulata-infected cells (TaH) presented ovalbumin (as measured by [3H]thymidine incorporation) to both resting autologous bovine T cells and ovalbumin-specific bovine CD4+ T cell lines. However, the former cells were also stimulated by TaH without exogenous antigen although to a lesser degree than in the presence of antigen. This "nonspecific" proliferation was not seen with the ovalbumin-specific T cell lines. The magnitude of response by resting T cells in the presence of antigen, to TaH or purified peripheral blood monocytes, was essentially similar. However, on a per cell basis fewer TaH were required. Considerably greater proliferation to antigen was seen with the ovalbumin-specific T cell lines in the presence of TaH compared to monocytes and again fewer TaH were required to elicit a response. The kinetics of processing did not appear to be substantially altered in TaH and the increased proliferation may be due to the elevated MHC class II expression of these cells. Genetic restriction studies with the T cell lines indicated that the restricting elements used to present ovalbumin by TaH were the same as those used by monocytes, as identified by an isoelectric focusing technique. The continuously growing cell lines provide us with a unique model for investigating parasite-accessory cell interactions in theileriosis. The augmented antigen presenting cell activity of TaH may play an important role in the pathogenesis of the disease. TaH will also provide us with a valuable resource for our antigen presentation studies. In particular, the enhanced antigen presentation by TaH enabled us to detect responses to lower levels of antigen, often an important consideration for experiments where the quantity of antigen available is the major limiting factor.

Tannic-acid staining material on high endothelial venules and lymphocytes in skin and peripheral lymph nodes in Staphylococcus aureus-associated erythroderma

The recognition and binding of glycoprotein receptors on lymphocytes to specific antigens present on high endothelial venules (HEV) precedes the egress of lymphocytes from the blood stream into the tissues. In this paper, we report the presence of HEVs with tannic-acid staining material (TASM+ HEVs) in Staphylococcus aureus-associated erythroderma, which allow the migration of CD8+ lymphocytes from the bloodstream into the epidermis. TASM positivity is also expressed on lymphocytes within the regional lymph nodes, and by intravascular lymphocytes prior to leaving the TASM+ HEV. It is proposed that TASM positivity may represent a molecule, which may function in binding lymphocytes to HEVs prior to egress from the HEV. (TASM is lost from lymphocytes after leaving the HEVs). The expression of TASM positivity may form an essential part of the CD8+ lymphocyte-HEV recognition system, and may be the means whereby CD8+ lymphocytes generated in the regional lymph nodes by various mitogens (in this case by staphylococcal mitogens) may 'home' to specific sites within the epidermis. TASM positivity on both the HEVs and lymphocytes may serve as a convenient marker of such a system.

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.

Differing regulation and function of ICAM-1 and class II antigens on renal tubular cells

Intercellular adhesion molecule-1 (ICAM-1) and MHC class II (Ia) antigens are increased on proximal tubular epithelial cells (TEC) in autoimmune nephritis and transplant rejection. ICAM-1 is a member of the immunoglobulin gene superfamily that increases the avidity of T cell interactions with antigen-presenting cells bearing Ia antigens. Using an existing mAb and cDNA probe for Ia antigen, and a newly described mAb (YN1/1.7.4) and cDNA probe for murine ICAM-1, we compared mRNA transcript levels, surface expression and function of these molecules in transformed TEC derived from normal (C3H/FeJ) and autoimmune (MRL-lpr) mice. No differences were found on TEC between these strains of mice. Stimulation of TEC with interferon-gamma (IFN-gamma) resulted in the expression of Ia antigens, and a marked increase of ICAM-1 from basal levels. Increases in ICAM-1 levels occurred with concentrations of IFN-gamma 10 to 100 times lower (0.5 to 1.0 U/ml) than those required for Ia expression, and preceded Ia antigen expression by more than 48 hours. Anti-ICAM-1 mAb lowered the binding and antigen-presenting ability of TEC to the A2A2 T cell hybridoma, suggesting a role for ICAM-1 in immune interactions between TEC and T cells. Dexamethasone treatment of MRL-lpr mice abrogated the increase of Ia antigens found in the kidneys of nephritic mice yet did not reduce the expression of ICAM-1 in either kidneys or cultured stimulated TEC. We conclude that elevated ICAM-1 expression on TEC increases the immune accessory cell capability of TEC bearing Ia antigens, and is resistant to down-regulation by some immunosuppressive agents.

Phorbol esters induce differentiation of U-937 human promonocytic cells in the absence of LFA-1/ICAM-1-mediated intercellular adhesion

Intercellular adhesions which occur during the mononuclear phagocyte differentiation are predominantly mediated by the lymphocyte-function-associated antigen-1 (LFA-1) family and the intercellular-adhesion molecule-1 (ICAM-1) which is a ligand for LFA-1. Thus, differentiation of U-937 promonocytic cells induced by phorbol esters occurs concomitantly with intercellular LFA-1/ICAM-1-dependent cluster formation. Since these homotypic adhesions can be inhibited by monoclonal antibodies (mAb) directed to either LFA-1 or ICAM-1, we have analyzed whether the lack of cell-cell adhesions impairs the differentiation process. Treatment of U-937 cells with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate in the presence of mAb to LFA-1 or ICAM-1 antigens yielded cells free from homotypic adhesions but differentiated as evidenced by their decreased proliferation and enhanced capacity for generation of superoxide anion. In addition, expression of the CD11c antigen was increased, whereas the transferrin receptor disappeared from the cell surface. Vimentin gene transcription was also greatly augmented as opposed to a clear diminution in the levels of c-myc and ornithine decarboxylase transcripts. These results clearly demonstrate that phorbol esters can induce differentiation of monocytic cells independently of cell-cell adhesion.

Cytokine-induced generation of multinucleated giant cells in vitro requires interferon-gamma and expression of LFA-1

Multinucleated giant cells (MGC), which are a common feature of various pathologic states, were generated in vitro by cytokine-stimulation of human peripheral blood monocytes. As expected, conditioned medium, i.e. the supernatant of concanavalin A-stimulated peripheral blood mononuclear cells, readily caused generation of MGC. Addition of a monoclonal antibody (mAb) against interferon-gamma (IFN-gamma) completely abrogated this effect. IFN-gamma alone, however, had a much smaller effect than the conditioned medium. All other cytokines tested [including interleukin (IL)2, IL4 and tumor necrosis factor-alpha, which are known to activate monocytes] did not induce MGC nor did they enhance the effect of IFN-gamma. Formation of MGC could almost entirely be inhibited by mAb to the alpha or beta chain of LFA-1 and to a lesser extent by relatively high concentrations of a mAb against ICAM-1, one of the ligands of LFA-1. In contrast to the anti-IFN-gamma mAb that had no significant effect on the formation of monocyte clusters, mAb against LFA-1 inhibited clustering very efficiently. Antibodies directed to a number of different antigens present on the surface of monocytes (alpha chains of CR3 and CR4, HLA class I and II molecules, CD14 and CD16 antigens) had little or no effect on the generation of MGC. IFN-gamma, but not the concanavalin A-induced supernatant clearly enhanced expression of LFA-1 and ICAM-1 on monocytes. The results indicate that cytokine-induced generation of MGC is not possible without IFN-gamma, but most probably additional factor(s) enhance this effect. The mechanism(s) by which IFN-gamma promotes monocyte fusion apparently includes, among others, up-regulation of LFA-1 whose expression seems to be necessary but not sufficient for fusion.

Adhesion molecules on the plasma membrane of epidermal cells. II. The intercellular adhesion molecule-1 is constitutively present on the cell surface of human resting Langerhans cells

The intercellular adhesion molecule-1 (ICAM-1), which is a member of the immunoglobulin superfamily, is expressed on many cell types, including a variety of cells showing accessory/antigen-presenting capacities and belonging to the monocyte/macrophage or dendritic lineages. Here it is shown that human freshly isolated Langerhans cells (LC) constitutively express ICAM-1, as expected. It seems likely that the amounts of ICAM-1 moieties expressed on the plasma membrane of resting LC are only limited, since they virtually escaped detection by conventional immunofluorescence procedures on epidermal sheets. However, all the observed Birbeck granule-bearing LC showed their clear, although relatively weak, ICAM-1 positivity when more sensitive techniques were employed, such as colloidal gold-immunoelectronmicroscopy using gold particles 15nm in size and, to an even higher extent, using gold particles 5 nm in size. Because ICAM-1 is a ligand for the adhesive molecule LFA-1, which is expressed on the surface of leukocytes and, especially, lymphocytes, the ICAM-1 (LC)/LFA-1 (T-lymphocytes) interactions might, enabling these cells to adhere together, deliver activation signals to T cells, thus constituting the initial event in the generation of a cutaneous immune response.

Human memory T cells express intercellular adhesion molecule-1 which can be increased by interleukin 2 and interferon-gamma

We have shown that low levels of intercellular adhesion molecule-1 (ICAM-1) expression can be detected on approximately 40% of the resting peripheral blood T cell population. The ICAM-1+ T cells have the phenotypic markers of memory cells which can be distinguished functionally from naive T cells by their ability to respond rapidly to previously experienced antigen. These cells appear to be in a state of marginal activation in that they also express low levels of the interleukin 2 receptor (Tac antigen) and have increased cell size as compared to the naive T cells. In addition we have shown that the cytokines interleukin 2 and interferon-gamma, both of which are products of activated T cells, are able to increase the expression of ICAM-1 on T cells. Finally, pretreating T cells with an anti-ICAM-1 monoclonal antibody inhibits their response to recall antigens, strongly suggesting a functional role for this protein on the memory T cell.

The induction of intercellular adhesion molecule 1 (ICAM-1) expression on human fetal astrocytes by interferon-gamma, tumor necrosis factor alpha, lymphotoxin, and interleukin-1: relevance to intracerebral antigen presentation

Antigen presentation reactions are dependent upon the expression of the class II major histocompatibility antigens (MHC), the T-cell receptor, and the presented antigen. Recent studies demonstrate that such processes also require the presence of adhesion molecules such as lymphocyte functional antigen 1 (LFA-1) and its cell surface ligand, intercellular adhesion molecule 1 (ICAM-1). It has been suggested that the brain astrocyte can function as a facultative antigen presenting cell (APC). This hypothesis is based upon the ability to induce the expression of the class II MHC antigens on astrocytes, and on their ability to present myelin basic protein to encephalitogenic T-cells in vitro. The best in vivo data showing that astrocytes serve as intracerebral APCs is the finding that astrocytes in multiple sclerosis plaques are DR+ (class II MHC in human). However, it still remains to be resolved whether the in vivo expression of the MHC antigens in disease states is instrumental to antigen presentation mechanisms or whether these cell surface glycoproteins are expressed secondary to brain immune responses. If astrocytes function as immunocompetent APCs within the brain, it would seem that they would also be able to express molecules important for intercellular adhesion. Here, we present the first data that indicates that human astrocytes are capable of expressing ICAM-1 in response to cytokines that either induce or upregulate the expression of DR. In essence, cytokines derived from different cell types seem to exert similar pleiotropic effects on the modulation of MHC and ICAM-1 expression on astrocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigen presenting cells

A great deal has been learned over the past few years regarding the molecular biology of antigen presentation. These discoveries have been possible in part because of acquisition of protein sequencing data regarding class I and class II MHC molecules and in part because of X-ray crystallographic analysis of the three-dimensional structures of these molecules. These discoveries have merged nicely with detailed immunologic studies delineating the 'minimal antigenic peptides' of complex protein antigens. All of these studies strongly confirm the belief that the antigen-specific interaction of T cells with antigen in the context of antigen presenting cells is exquisitely specific. The process of 'trimolecular complex' formation involves binding interactions between antigenic peptide, class I or class II MHC molecules and the antigen-specific T cell receptor. One of the key functions of antigen presenting cells involves the 'processing' of complex protein antigens so as to allow for the interaction of the 'minimal antigenic peptide' with the appropriate class I or class II MHC molecule. A substantial body of evidence now indicates that the interaction of processed antigenic peptides and class II MHC molecules involves a binding interaction with a significant binding affinity and a slow dissociation constant. In addition to antigen-specific binding interactions which govern antigen presentation, there are a variety of antigen-independent and MHC-independent factors which greatly augment the process of antigen presentation. Along with differences in antigen processing, these factors probably account for the qualitative and quantitative differences seen between the various cell types involved in antigen presentation. There may be a substantial amount of antigen which associates with the antigen presenting cell surface in an MHC-independent fashion associated with so-called 'non-MHC peptide binding structures'. However, if the trimolecular complex theory is to be satisfied, antigen bound to these structures ultimately must become associated with the MHC restricting element in order to effectively engage the antigen-specific T cell receptor. Antigen presenting cells differ in their sensitivity to lymphokines and inflammatory mediators which augment antigen presentation. In addition, antigen presenting cells differ in their capacity to secrete or express membrane-bound costimulatory molecules, such as interleukin 1. Finally, factors which promote the cellular adherence of antigen presenting cells with T cells greatly augment the process of antigen presentation.(ABSTRACT TRUNCATED AT 400 WORDS)

Cotransfection of ICAM-1 and HLA-DR reconstitutes human antigen-presenting cell function in mouse L cells

The initiation of a specific immune response is believed to require not only activation through antigen-specific receptors on T cells and B cells but also antigen-independent interactions between accessory molecules. One such molecule is LFA-1, which enhances the avidity of interactions between T cells and antigen-presenting cells, and is possibly involved in signal transduction across the T-cell membrane. Intercellular adhesion molecule-1 (ICAM-1), a surface glycoprotein of relative molecular mass (Mr) 80,000-110,000, has been defined as a ligand for LFA-1, and has been shown to participate in the interaction between T cells and monocytes. The determination of the precise contribution of such accessory molecules to antigen presentation, however, is complicated by the need to analyse against a background of multiple molecular interactions. We have investigated the role of LFA-1/ICAM-1 interactions in antigen presentation directly by quantifying the contribution of ICAM-1 expression to T-cell stimulation using L-cell transfectants that co-express ICAM-1 and HLA-DR. In the case of transfectants expressing modest levels of HLA-DR, co-expression of ICAM-1 is critical for effective HLA class II-restricted and allospecific T-cell activation, pointing to an important role for ICAM-1 in the induction of T-cell responses.

Human tonsillar dendritic cell-induced T cell responses: analysis of molecular mechanisms using monoclonal antibodies

Dendritic cells, isolated from human tonsillar tissue, were found to be potent stimulators of the sodium periodate T cell oxidative mitogenesis reaction. Monoclonal antibodies against CD2, CD4, CD11a, CD18, LFA-3, ICAM-1, class I and class II major histocompatibility complex (MHC) inhibited T cell proliferation in this response, whereas antibodies against CD8, CD11b, CD11c and CD16 had no effect. Further, antibodies against CD2, CD11a, CD18, LFA-3 and ICAM-1 inhibited the early dendritic cell-T cell clustering event which occurs in this cell interaction. In contrast, antibodies against CD4, class I and class II MHC did not inhibit clustering. Studies examining the expression of the respective molecules upon isolated dendritic cells and T cells suggest that anti-LFA-3 and anti-class II MHC antibodies inhibit at the level of the dendritic cell, whereas anti-CD2 and anti-CD4 antibodies inhibit at the level of the T cell. However, antibodies against CD11a, CD18, ICAM-1 and class I MHC may inhibit at either or both cell levels. These findings have enabled us to propose a molecular mechanism for dendritic cell-T cell interaction in oxidative mitogenesis. Dendritic cell-T cell clustering is mediated by bidirectional binding of LFA-1 (CD11a and CD18) and ICAM-1 (involving both molecules on both cell types) and unidirectional binding of CD2 and LFA-3 (involving T cell CD2 and dendritic cell LFA-3). This initial event permits a second interaction of dendritic cell and T cell molecules, involving T cell CD4, class I MHC (possibly at both cellular levels) and dendritic cell class II MHC, which deliver the signal for proliferation.

Astrocytes and intracerebral immune responses

The astrocyte is the most abundant cell within the central nervous system (CNS). This cell subserves a multiplicity of important functions that contribute to the process of neural development as well as to the integrity of normal brain function. Adding to the already exhaustive list of capabilities, the astrocyte has now been demonstrated to function as an intracerebral antigen presenting cell. These findings are serving to revise our view of the brain as an immunoprivileged site and perhaps will shed some light on the pathogenetic mechanisms involved in a number of CNS disorders of immune dysregulation. In this review we provide some perspective on the regulatory mechanisms that influence astrocyte immune functions. Specifically, we address the role played by the major histocompatibility complex (MHC) antigens as well as adhesion molecules in the initiation of brain immune responses.

Schwann cells co-cultured with stimulated T cells and antigen express major histocompatibility complex (MHC) class II determinants without interferon-gamma pretreatment: synergistic effects of interferon-gamma and tumor necrosis factor on MHC class II induction

Schwann cells (SC) do not express major histocompatibility complex (MHC) class II antigens under normal culture conditions. SC can, however, be induced in vitro to express MHC class II molecules by exposure to high concentrations of interferon-gamma (IFN-gamma) and can present antigens to antigen-specific T cell lines. In the present study immunohistochemical labeling showed that most SC (greater than 90%) prepared from rat neonatal sciatic nerves expressed MHC class II molecules when cultured together with mycobacterial antigen and T cells, and as a consequence were able to function as antigen-presenting cells in lymphoproliferation assays, without requiring pretreatment with IFN-gamma. Antigen or T cells alone were ineffective in stimulating MHC class II expression and induction of class II molecules was MHC restricted, requiring the presence of syngeneic T cells. Addition of monoclonal antibody DB1, directed against IFN-gamma to co-cultures of SC and T lymphocytes stimulated with antigen, prevented the induction of MHC class II antigen on SC. When SC were incubated with recombinant (r)IFN-gamma alone, up to 50% of SC showed positive labeling for MHC class II antigen. This level of expression was enhanced to greater than 80% when recombinant tumor necrosis factor (rTNF) was also added. rTNF alone had no effect, and addition of DBI antibody inhibited the synergistic effects of rTNF on MHC class II expression. The effects of rIL 4 were also investigated but neither rIL 4 alone nor rIL 4 in combination with rIFN-gamma induced MHC class II expression by SC. These results show that in the presence of sensitized T lymphocytes and antigen, SC do not require pretreatment with exogenous rIFN-gamma to express MHC class II antigens and function as antigen-presenting cells. T cell-derived TNF and IFN-gamma appear to act as mediators of the T cell-induced expression of MHC class II by SC.

Identification of a novel monocyte cell surface molecule involved in the generation of antigen-induced proliferative responses

A monocyte molecule, identified by a monoclonal antibody (mAb) named 24, is involved in the antigen-specific proliferation of T cells. Several types of antigen-induced responses are blocked by mAb24, but mitogen responses, even at low doses, are not. The 24 molecule is found on circulating monocytes and no other cell type. Normally only a proportion of monocytes express the 24 molecule but it can be induced rapidly on monocytes in culture, possibly from intracellular sources. The epitope is present on a heterodimer of 175 and 95 kDa which is similar to the leukocyte cell adhesion molecule (Leu-CAM) family. These findings suggest that although the 24 molecule shows some functional and biochemical similarities with the Leu-CAM family of molecules, it represents a novel structure primarily associated with mononuclear phagocytes.

Importance of an 85 kDa membrane glycoprotein for a variety of cell-cell interactions

The membrane molecule termed "7F7-antigen" has been found to be involved in several examples of cell-cell interactions. This 85 kDa glycoprotein with a protein core of about 55 kDa contains N-linked and O-linked carbohydrates. It has an isoelectric point of 8.0-8.5 and is expressed on 20% of peripheral blood mononuclear cells, 35% of peripheral blood B-cells, follicular dendritic cells and vascular endothelium. It is also expressed on activated T-cells and its expression on B-cells, fibroblasts and monocytes increases after treatment with PWM, interferon-gamma and after three days culture, respectively. The MAb 7F7 used to define this antigen inhibits the initiation of T-cell proliferation induced by anti-CD3, PHA, ConA and (weakly) allogenic stimulator cells, but does not affect the growth of IL-2 dependent T-cells and does not interfere with the killing of PHA-blasts by allogenic IL-2 dependent T-cells. 7F7 also inhibits the binding of C3-coated sheep erythrocytes to B-cells, the PMA-induced aggregation of U937 and the binding of activated T-cells to fibroblasts. The 7F7-antigen is expressed on some non-Hodgkin lymphomas of B-cell differentiation, particularly those with follicular structure, but not on Burkitt's lymphoma, ALL or carcinomas of various tissues. It is, however, found on fibrous tissue surrounding infiltrating carcinoma cells. The expression of a melanoma antigen, P3.58, which was shown to be identical to 7F7-antigen correlates with stage and spread of invasive melanoma. It was concluded that the 7F7-antigen, which is probably related to a previously described adherence molecule (ICAM-1), is of biological importance for the initiation of T-cell responses. With the possible exception of melanoma its expression on neoplastic cells in vivo is unlikely to be of importance for the spread of malignant disease.

The role of lymphocyte function-associated antigen 1 (LFA-1) in the adherence of T lymphocytes to B lymphocytes

The functional role of the LFA-1 molecule in the interaction between helper T lymphocytes and B lymphocytes was investigated using lymphocytes from patients with leukocyte adhesion deficiency, an inherited immunodeficiency characterized by a defective leukocyte expression of the LFA-1, Mac-1 (CR3) and p150,95 molecules. The ability of LFA-1- T lymphocytes to provide antigen-specific help for HLA-identical LFA-1+ B lymphocytes was reduced while their antigen-specific activation was normal. Antigen-independent conjugate formation between resting, nonactivated LFA-1- T lymphocytes and LFA-1+ B lymphocytes was impaired while LFA-1- B lymphocytes bound LFA-1+ T lymphocytes normally. Conjugate formation of activated LFA-1- T lymphocytes was mostly mediated by the CD2-LFA-3 adhesion pathway while the ICAM-1 molecule, a ligand of LFA-1, had no function. These results demonstrate that LFA-1 plays a major role in the cognate interaction between helper T lymphocytes and B lymphocytes that cannot be mediated instead by CD2 or other molecules on resting T lymphocytes.