Crosslinking of the CD5 antigen on human T cells induces functional IL2 receptors

Defective STAT5 Activation and Aberrant Expression of BCL6 in Naive CD4 T Cells Enhances Follicular Th Cell-like Differentiation in Patients with Granulomatosis with Polyangiitis

Granulomatosis with polyangiitis (GPA) is a potentially fatal small vessel vasculitis of unknown etiology, characterized by anti-neutrophil cytoplasmic autoantibodies, chronic inflammation, and granulomatous tissue damage. T cell dysregulation, comprising decreased regulatory T cell function and increased circulating effector memory follicular Th cells (TFH), is strongly associated with disease pathogenesis, but the mechanisms driving these observations are unknown. We undertook transcriptomic and functional analysis of naive CD4 T cells from patients with GPA to identify underlying functional defects that could manifest in the pathogenic profiles observed in GPA. Gene expression studies revealed a dysregulation of the IL-2 receptor β/JAK-STAT signaling pathway and higher expression of BCL6 and BCL6-regulated genes in GPA naive CD4 T cells. IL-2-induced STAT5 activation in GPA naive CD4 T cells was decreased, whereas STAT3 activation by IL-6 and IL-2 was unperturbed. Consistently, BCL6 expression was sustained following T cell activation of GPA naive CD4 T cells and in vitro TFH differentiation of these cells resulted in significant increases in the production TFH-related cytokines IL-21 and IL-6. Thus, naive CD4 T cells are dysregulated in patients with GPA, resulting from an imbalance in signaling equilibrium and transcriptional changes that drives the skewed pathogenic CD4 effector immune response in GPA.

CD5 levels define functionally heterogeneous populations of naïve human CD4+ T cells

Studies in murine models show that subthreshold TCR interactions with self‐peptide are required for thymic development and peripheral survival of naïve T cells. Recently, differences in the strength of tonic TCR interactions with self‐peptide, as read‐out by cell surface levels of CD5, were associated with distinct effector potentials among sorted populations of T cells in mice. However, whether CD5 can also be used to parse functional heterogeneity among human T cells is less clear. Our study demonstrates that CD5 levels correlate with TCR signal strength in human naïve CD4⁺ T cells. Further, we describe a relationship between CD5 levels on naïve human CD4⁺ T cells and binding affinity to foreign peptide, in addition to a predominance of CD5^hi T cells in the memory compartment. Differences in gene expression and biases in cytokine production potential between CD5^lo and CD5^hi naïve human CD4⁺ T cells are consistent with observations in mice. Together, these data validate the use of CD5 surface levels as a marker of heterogeneity among human naïve CD4⁺ T cells with important implications for the identification of functionally biased T‐ cell populations that can be exploited to improve the efficacy of adoptive cell therapies.

Absence of CD5 dramatically reduces progression of pulmonary inflammatory lesions in SHP-1 protein-tyrosine phosphatase-deficient 'viable motheaten' mice

Mice homozygous for the viable motheaten (Hcph(me-v)) mutation are deficient in SHP-1 protein-tyrosine phosphatase, resulting in severe systemic autoimmunity and immune dysfunction. A high percentage of B-cells in viable motheaten mice express the cell surface glycoprotein CD5, in contrast to wild type mice that express CD5 on only a small percentage of B-cells. CD5(+) B-cells have been associated with autoantibody production. To determine the role of CD5 in the development of the inflammatory disease in me(v)/ me(v) mice, we created a stock of CD5(null)me(v)/ me(v) mice. The longevity of CD5(null)me(v)/ me(v) mice was increased 69% in comparison to me(v)/ me(v) mice on a similar (B6;129) background. The increased lifespan was associated with a marked reduction in pulmonary inflammation. Flow cytometry analysis of spleen cells from CD5(null)me(v)/ me(v) mice at 9-12 weeks of age revealed significant decreases in percentages of IgM/B220 double positive B-cells, Mac-1/Gr-1 double positive cells and CD4(+) T-cells compared with me(v)/ me(v) mice. CD5(null)me(v)/ me(v) mice also had significantly lower serum IgM levels in comparison to me(v)/ me(v) mice. Study of CD5(null)me(v)/ me(v) mice may provide further insight into the role of CD5 in cell signaling and may help explain the observed association of CD5(+) B-cells with autoimmune disease.

Apoptosis induction by hypercross-linking of the surface antigen CD5 with anti-CD5 monoclonal antibodies in B cell chronic lymphocytic leukemia

We evaluated cells from 24 patients with B cell chronic lymphocytic leukemia (B-CLL) to determine apoptosis induced by CD5 hypercross-linking. Following the CD5 hypercross-linking with anti-CD5 monoclonal antibodies (MoAbs), we identified 10 patients where CD5 hypercross-linking induced apoptosis (group A) and 14 patients whose cells were resistant to the anti-CD5 MoAbs (group B). The programmed cell death pathway of the cells from patient group A was caspase-3 and poly (ADP-ribose) polymerase (PARP)-dependent, involved a reduction of the mitochondrial transmembrane potential DeltaPsi and a down-regulation of the anti-apoptotic Bcl-2, Mcl-1 and iNOS proteins. Early activation-associated molecules such as CD25 and CD69 were expressed at higher levels than in controls after 6 h of culture with anti-CD5 MoAb. The expression of CD5 and of CD72, the ligand for CD5, were significantly lower in group A compared with group B. Anti-CD20 MoAb had similar activity with anti-CD5 MoAb and the combination of the two MoAbs seemed to be additive. In this study, it is suggested that the cells from some B-CLL patients can be induced into programmed cell death by CD5 hypercross-linking with anti-CD5 MoAbs.

Anti CD5 sustains the proliferative response of IgM-activated human CD5+ B cells

The CD5 molecule is expressed by most T cells but it is present on a minor B cell subset. Whilst several studies have provided information on the physiological role of T cell CD5, the functional role of CD5 on B lymphocytes remains unclear. To address this question, tonsillar CD5+ B cells were sorted by dual-colour fluorescence and FACS. Sorted cells were stimulated with polyclonal anti-IgM antibodies (Ab), and monoclonal (MoAb) F(ab')2 fragments of anti-CD5. Proliferative responses were evaluated by enumeration of Ki-67 positive cells using quantitative flow cytometry. Co-stimulation with anti-CD5 MoAb for 3 days did not affect the anti-IgM and IL2-induced proliferation of CD5+ B cells. This was seen under conditions where the anti-CD5 was soluble, adsorbed to the microwells or cross-linked by anti-mouse antibodies. Fewer CD25+ cells were detected, however, in the presence of anti-CD5. In contrast, the proliferative response of CD5+ B cells prestimulated for 3 days with IL-2 and anti-IgM, was sustained in a further 3-day culture period when anti-CD5 was added. It is concluded that CD5 occupancy might provide an additional signal to activated CD5+ B cells favouring their proliferation and differentiation into autoantibody secreting cells.

Characterization of new monoclonal antibodies identifying avian T lymphocyte antigens

Six monoclonal antibodies (mAb) were produced to identify and characterize surface antigens of chicken T cells. Determination of their reactivity with different lymphatic cells using immunofluorescence analysis demonstrates that mAb KH8, NA6, PD4 and TH8 stained 32-43% blood lymphocytes, 72-77% thymocytes and 19-27% spleen cells, mAb OC5 approximately 99% thymocytes and 55% blood and spleen lymphocytes each, and mAb OC2 36% blood lymphocytes, 79% thymocytes and 62% spleen cells. The KH8, NA6, PD4 and TH8 antibodies immunoprecipitated from lysates of surface-labeled chicken thymocytes a polypeptide of M(r) 60,000 under non-reducing conditions and the OC5 antibody a glycoprotein of M(r) 68,000 under reducing conditions. MAb OC2 precipitated a single polypeptide of M(r) 40,000 under both conditions. The mAb KH8, NA6, PD4, TH8 and OC2 inhibited ConA-induced proliferative responses of blood T cells in vitro. However, sepharose-bound or soluble OC5 antibody was able to increase DNA synthesis significantly. These results indicate that (a) the mAb KH8, NA6, PD4 and TH8 identify the avian homologue of the mammalian CD4 molecule, (b) the mAb OC2 detects the avian CD2 antigen, and (c) the mAb OC5 recognizes the putative avian CD5 homologue.

Staphylococcal enterotoxin enhances the activation of rat encephalitogenic T cells by myelin basic protein

It is generally believed that the activation of autoreactive T cells is an essential step in the pathogenesis of autoimmune diseases; however, autologous antigens are often weak immunogens and their detectable levels in vivo are much lower than required for T-cell activation. In experimental autoimmune encephalomyelitis, encephalitogenic T cells specific for myelin basic protein (MBP) react weakly to autologous rat myelin basic protein (RBP) but strongly to guinea pig-derived basic protein, even though both ligands possess the essential epitope (MBP(68-88)). Here we demonstrate that RBP is converted to a strong immunogen in the presence of a small dose of bacterial superantigen, staphylococcal enterotoxin E (SEE). The enhancing effect of SEE on the rat protein was apparent with all encephalitogenic T-cell lines examined in this study, including those not responding to RBP alone. It depended, moreover, on the simultaneous presence of RBP and SEE; delaying the addition of SEE for 8-12 h greatly decreased the potency of RBP. None of a series of major cytokines was able to replace SEE as an enhancer. Our results indicate that two T ligands, one a bacterial superantigen, can interact to enhance the activation of autoreactive T cells. This observation has implications for the involvement of bacterial and viral infections in the pathogenesis of multiple sclerosis.

Transfection of TCR alpha/beta genes in T cell hybridoma induces expression of CD5 molecules and increases allogenic proliferative and cytotoxic response

In the present work, we have studied the activity in vitro of T cell hybridoma (DO11107) in which the alpha/beta TCR genes of a cytotoxic T cell clone (KB5C20) were transfected. All clones transfected expressed CD5 molecule and have an important proliferative and cytotoxic allogenic activity.

Inhibition of synovial fluid T cell proliferation by anti-CD5 monoclonal antibodies. A potential mechanism for their immunotherapeutic action in vivo

OBJECTIVE

Monoclonal antibodies (MAb) directed against the T cell surface molecule CD5 are able to provide accessory stimulatory signals to resting T cells. The potential role of CD5 as an immunoregulatory molecule in inflammatory synovitis was examined.

METHODS

Synovial fluid and peripheral blood T cells of patients with active rheumatoid arthritis (RA) were purified and stimulated with interleukin-2 (IL-2), and the effect of MAb directed against CD5 on IL-2 responsiveness was examined.

RESULTS

IL-2-induced proliferation of synovial fluid T cells was strongly inhibited by anti-CD5 MAb, but not by anti-CD28 or anti-CD3 MAb. In RA peripheral blood T cells, MAb directed against CD5, CD3, and CD28 induced IL-2-dependent T cell growth, similar to findings in healthy controls. The difference in activity of anti-CD5 MAb on synovial fluid T cells compared with peripheral blood T cells was not due to different surface expression of CD5.

CONCLUSION

Anti-CD5 has an inhibitory effect on in vivo-activated synovial fluid T cells. The disease-ameliorative effects of anti-CD5 immunotoxin treatment of RA may be partly due to "switching-off" of T cell activation in the joints.

The B-cell surface protein CD72/Lyb-2 is the ligand for CD5

The glycoprotein CD5 is expressed on the surface membrane of all mature T cells and a small proportion of B lymphocytes. Its exact role in immune interactions is still unknown. Studies indicate that CD5 functions both in mice and humans as a receptor, delivering co-stimulatory signals to T cells in a manner similar to CD2 (ref. 11) and CD28 (ref. 12). Anti-CD5 antibodies stimulate both T-cell proliferation mediated by CD3 in association with the T-cell receptor and secretion of interleukin-2 and expression of its receptor, as well as inducing an increase in intracellular Ca2+ concentration (refs 5-10). To identify the ligand for CD5 we purified the human CD5 protein, labelled it with biotin and used it as a probe. Here we report that CD5 specifically interacts with the cell-surface protein CD72 exclusive to B cells. This interaction is blocked by anti-CD72 antibodies, but not by any other anti-B-cell antibodies. Moreover, non-B cells (mouse L-cell fibroblasts and human Jurkat T cells) expressing a transfected human CD72 complementary DNA could bind to the CD5-biotin conjugate. The results demonstrate that the B-cell surface protein CD72 (Lyb-2 in mice) is the ligand for CD5.