Role of LFA-1, CD2, VLA-5/CD29, and CD43 surface receptors in CD4+ T cell adhesion to B cells.

We investigated the adhesion to B cells of CD4+ T cells both in the resting state and following activation by CD3 cross-linking or stimulation by PMA/ionomycine/IL2 for 6 days. Both resting and activated CD4+ T cell adhesion were inhibited by anti-LFA-1, -CD2, -VLA-5/CD29, and -CD43 antibodies, suggesting coordinated upregulation of T cell adhesion. The CD2 and LFA-1 adhesion pathways were found to act independently, as CD2 was functional in T cells not expressing LFA-1, and vice versa, and as specific antibodies had additive effects. In contrast, LFA-1- and VLA-5/CD29-specific antibodies did not have an additive blocking effect on CD4+ T cell adhesion, suggesting that efficient adhesion requires a competitive association of integrins with cytoskeleton elements. Although the involvement of fibronectin (coated to B cells via VLA-4) in VLA-5-mediated T cell adhesion to B cells is feasible, an anti-fibronectin and a VLA-4-specific antibody had no blocking effect. The involvement of an unidentified B cell ligand can also be envisaged.

Differential CD4-dependent regulation of naive and memory CD4+ T cell adhesion is not related to differences in expression and function of CD4 and p56lck.

We have previously reported that antigen-independent adhesion of CD45RO+ memory CD4+ T cells to B cells is negatively regulated by CD4-MHC class II interaction, whereas that of CD45RA+ naive CD4+ T cells is not. We have now found that both cross-linking of CD4 ligands [anti-CD4 mAbs, HIV gp160 (env) protein and a 12mer peptide encompassing the 35-46 sequence of the HLA-DR beta 1 domain] on CD4+ naive T cells and activation-induced conversion of naive CD4+ T cells to memory T cells leads to CD4-dependent down-regulation of adhesion. To further elucidate CD4-dependent differential regulation of naive and memory T cell adhesion to B cells, we investigated the expression and function of CD4 and p56lck, a tyrosine kinase associated with the cytoplasmic domain of CD4. p56lck tyrosine kinase activity was equally enhanced by anti-CD4 mAbs and gp160 (120) in the two subsets. Furthermore, cell-surface CD4 down-modulation by phorbol myristate acetate or anti-CD4 mAbs was similar in the two subsets, which express the same amounts of both cell-surface CD4 and CD4-associated p56lck. Finally, the pattern of tyrosine phosphorylation of cellular proteins induced by gp120 (160) was similar in the two subsets. Taken together, these results indicate that the different sensitivity of naive and memory CD4+ T cells to CD4-dependent regulation of adhesion is not accounted for by differences in the tyrosine kinase activity of p56lck; it probably, therefore, involves a step downstream of p56lck or another pathway differentially used in naive and memory CD4+ T cells.

Antigen-independent adhesion of CD4 CD45RA T cells from cord blood.

Antigen-independent adhesion of resting adult CD4+ CD45RO+ T cells to B lymphocytes has been shown to be transient and can be down-regulated by CD4 major histocompatibility complex (MHC) class II molecule interactions. Conversely, adhesion of adult CD4+ CD45RA+ subpopulation to B cells is not regulated by ligands of CD4. We have investigated the regulation of adhesion of cord blood CD45RA+ CD4+ T lymphocytes. In contrast to adult CD45RA+ CD4+ T cells, cord blood CD45RA+ CD4+ T cells were strongly sensitive to the down-regulation of adhesion mediated by the CD4-HLA class II interaction, since adhesion to MHC class II(+) B cells was transient and inhibited by an anti-CD4 antibody. In addition, human immunodeficiency virus gp160, synthetic gp106-derived peptides encompassing a CD4 binding site inhibited conjugate formation between cord blood CD45RA+ CD4+ T cells and B cells. Following activation of the cord blood CD4 T cells by an anti-CD3 antibody, a conversion from a transient to a stable adhesion pattern of cord blood CD4 T cells to B cells occurred in 2 days. The reversal to a transient adhesion occurred at day 8 following anti-CD3 activation in correlation with a complete shift to a CD45RO phenotype of the cord blood CD4 T cells. These data suggest that CD4 T cell adhesion can be developmentally regulated.

GF109203X, a specific PKC inhibitor, abrogates anti-CD3 antibody-induced upregulation of CD4+ T cell adhesion to B cells.

Antigen-independent adhesion of CD4+ T lymphocytes to Epstein-Barr virus transformed B cells is mainly mediated by LFA-1 (CD11a/CD18) and CD2 molecules. Low-affinity binding of resting T cells can be transiently upregulated by cross-linking of CD3-TCR (T cell receptor) complexes. This inside-out signaling influences integrin (beta 1 and beta 2) adhesion capacity. Studies using the nonspecific inhibitor staurosporine have suggested that this phenomenon is dependent on protein kinase C activation. We found that the upregulation of anti-CD3-activated CD4+ T cell adhesion was inhibited strongly and in a concentration-dependent manner by GF109203X, a compound described as a potent and selective inhibitor of PKC. Comparative studies showed that GF109203X and staurosporine had similar inhibitory effects on the upregulation of activated CD4+ T cell adhesion. However, staurosporine is a nonselective kinase inhibitor. PMA-activated CD4+ T cell adhesion was also inhibited by GF109203X. In contrast, passive enhancement of adhesion by treatment with the CD11a-specific antibody NKI-L16 was unaffected by GF109203X. Taken together, these results show that PKC is involved in upregulating the adhesion of CD4+ T cells to B cells following activation of the former by CD3 cross-linking. PKC-dependent upregulation of CD4+ T cell adhesion to B cells is exclusively LFA-1-dependent, as GF109203X had no additional inhibitory effect on anti-LFA-1 antibody-pretreated T cells activated by the anti-CD3 antibody OKT3 and had no effect on the adhesion of LFA-1(-) CD4+ T cells. Finally, PKC inhibition did not alter CD2-mediated adhesion. This points to a limited participation of CD2 in T-B cell interactions after TCR/CD3 cross-linking.

Antigen-independent adhesion of CD45RA (naive) and CD45RO (memory) CD4 T cells to B cells.

We found that naive (CD45RA+) CD4 T cells have a lower capacity of adhesion to Epstein-Barr virus (EBV) immortalized B cells than memory (CD45RO+) CD4 T cells, as judged by conjugate formation. This would appear to be due to differences in the expression of adhesion molecules [lymphocyte function-associated antigen (LFA)-1, CD2]. However, kinetic studies showed that the degree of adhesion of naive T cells to B cells was stable over 60 min while that of memory T cells, like that of unseparated CD4 T cells, was characterized by a rapid formation and rapid dissociation of conjugates. This could be explained by a difference in the sensitivity of naive and memory CD4 T cells to down-regulation of antigen-independent adhesion by CD4-MHC class II interaction. Indeed, memory T cells also adhered stably to MHC class II(-) B cells. The adhesion of memory T cells, but not naive T cells, to MHC class II(+) B cells was sensitive to inhibition by OKT4a an anti-CD4 antibody, human immunodeficiency (HIV) gp160 (env) protein and a 12-mer peptide encompassing the 35-46 sequence of the HLA, DR beta 1 domain and previously shown to inhibit activation of HLA class II-restricted CD4 T cell responses. Since MHC class II expression did not influence the degree of conjugate formation by naive or memory CD4 T cells with B cells, CD4-MHC class II interaction does not appear to be involved in binding itself, but may down-regulate the adhesion of memory but not naive CD4 T cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of T helper-B lymphocyte adhesion through CD4-HLA class II interaction.

Antigen-independent adhesion of CD4+ T lymphocytes to Epstein-Barr virus (EBV)-transformed B cells is mediated by CD2/lymphocyte function-associated antigen (LFA)-3 and LFA-1/intracellular adhesion molecule (ICAM)-1. Although some anti-CD4 antibodies block the antigen-independent adhesion of CD4+ T lymphocytes, the CD4-HLA class II interaction does not appear to significantly contribute to the forces of cell adhesion since CD4+ T cells equally bind HLA class II+ and HLA class II- mutant B cells. In addition, conjugates formed between CD4+ T cells and HLA class II- B cells remain stable for at least 1 h while CD4+T/HLA class II+ B cell conjugate percentages promptly drop off. Down-regulation of CD4 or spontaneous low expression of CD4 also results in a persistance of conjugates formed with B cells. The role of the CD4-HLA class II interaction has been further studied by investigating the inhibitory effect of synthetic 12-mer peptides analogous to HLA class II and containing the Arg-Phe-Asp-Ser sequence conserved in the beta 1 domain. These peptides were previously found to inhibit HLA class II-restricted T cell responses, this sequence being thought to be involved in CD4-HLA class II interaction. These peptides block conjugate formation of CD4+ resting T cells or clones but not of CD8+ T cells, by interacting with the T cells as shown by preincubation experiments. Down-regulation of CD4 or spontaneous low expression results in the loss of the inhibitory activity. The peptide-mediated inhibition is neutralized by a soluble dimeric CD4 molecule. Alteration within the Arg-Phe-Asp-Ser sequence results in a significant loss of inhibition. It is thus proposed that the CD4-HLA class II interaction negatively regulates antigen-independent adhesion of T cells, this interaction involving the highly conserved Arg-Phe-Asp-Ser sequence in the HLA class II beta 1 sequence as a CD4-binding site.

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.

[Fast immunochemical assay of proteins with Gemsaec centrifugal analyser. Application to serum transferrin and IgA assay]. / Dosage immunochimique rapide des protéines sur analyseur centrifuge gemsaec. Application au dosage de la transferrine et des IgA du sérum sanguin.

An automated method for measurement of specific proteins on a centrifugal analyser is reported. Based on the immunoprecipitin turbidimetric reaction enhanced by polyethylene-glycol, the technique, simple and fast, gives precise and accurate results with following cautions: the antigen and antibody concentrations must be carefully chosen according to defined specific antiserum, and two dilutions of each serum sample must be assayed to control quite satisfactory determination and exhibit any antigen excess error. Large series of serum transferrin and IgA assays were studied and compared with radial immunodiffusion and continuous-flow immunonephelometric method: good correlations prove the value of the reported method.