The 5C8 monoclonal antibody reacts with human and cynomolgus monkey CD154 also known as CD40 ligand. CD154 exists as a 39 kDa accessory molecule and belongs to the TNF superfamily of cytokines. CD154 is primarily expressed on the surface of activated CD4+ T lymphocytes but can also be expressed by platelets, mast cells, macrophages, basophils, NK cells, B lymphocytes, CD8+ T lymphocytes as well as non-hematopoietic cells including smooth muscle cells, endothelial cells, and epithelial cells. CD154 signals through CD40 and is thought to play a key role in T and B lymphocyte co-stimulation. The 5C8 monoclonal antibody has been reported to block CD40L-CD40 interactions.

INVIVOMAB ANTI-HUMAN/MONKEY CD40L (CD154) (CLONE: 5C8)

Nadazdin, O., et al. (2011). “Contributions of direct and indirect alloresponses to chronic rejection of kidney allografts in nonhuman primates.” J Immunol187(9): 4589-4597. PubMed

The relative contribution of direct and indirect allorecognition pathways to chronic rejection of allogeneic organ transplants in primates remains unclear. In this study, we evaluated T and B cell alloresponses in cynomolgus monkeys that had received combined kidney/bone marrow allografts and myeloablative immunosuppressive treatments. We measured donor-specific direct and indirect T cell responses and alloantibody production in monkeys (n = 5) that did not reject their transplant acutely but developed chronic humoral rejection (CHR) and in tolerant recipients (n = 4) that never displayed signs of CHR. All CHR recipients exhibited high levels of anti-donor Abs and mounted potent direct T cell alloresponses in vitro. Such direct alloreactivity could be detected for more than 1 y after transplantation. In contrast, only two of five monkeys with CHR had a detectable indirect alloresponse. No indirect alloresponse by T cells and no alloantibody responses were found in any of the tolerant monkeys. Only one of four tolerant monkeys displayed a direct T cell alloresponse. These observations indicate that direct T cell alloresponses can be sustained for prolonged periods posttransplantation and result in alloantibody production and chronic rejection of kidney transplants, even in the absence of detectable indirect alloreactivity.

Jabara, H. H., et al. (2001). “Glucocorticoids upregulate CD40 ligand expression and induce CD40L-dependent immunoglobulin isotype switching.” J Clin Invest 107(3): 371-378. PubMed

IL-4 and CD40 ligation are essential for IgE synthesis by B cells. We have shown previously that hydrocortisone (HC) induces IgE synthesis in IL-4-stimulated human B cells. In this study we demonstrate that HC fails to induce IgE synthesis in B cells from CD40 ligand-deficient (CD40L-deficient) patients. Disruption of CD40L-CD40 interactions by soluble CD40-Ig fusion protein or anti-CD40L mAb blocked the capacity of HC to induce IgE synthesis in normal B cells. HC upregulated CD40L mRNA expression in PBMCs and surface expression of CD40L in PBMCs as well as in purified populations of T and B cells. Upregulation of CD40L mRNA in PBMCs occurred 3 hours after stimulation with HC and was inhibited by actinomycin D. Upregulation of CD40L mRNA and induction of IgE synthesis by HC were inhibited by the steroid hormone receptor antagonist RU-486. These results indicate that ligand-mediated activation of the glucocorticoid receptor upregulates CD40L expression in human lymphocytes.

Singh, J., et al. (1998). “The role of polar interactions in the molecular recognition of CD40L with its receptor CD40.” Protein Sci 7(5): 1124-1135. PubMed

CD40 Ligand (CD40L) is transiently expressed on the surface of T-cells and binds to CD40, which is expressed on the surface of B-cells. This binding event leads to the differentiation, proliferation, and isotype switching of the B-cells. The physiological importance of CD40L has been demonstrated by the fact that expression of defective CD40L protein causes an immunodeficiency state characterized by high IgM and low IgG serum levels, indicating faulty T-cell dependent B-cell activation. To understand the structural basis for CD40L/CD40 association, we have used a combination of molecular modeling, mutagenesis, and X-ray crystallography. The structure of the extracellular region of CD40L was determined by protein crystallography, while the CD40 receptor was built using homology modeling based upon a novel alignment of the TNF receptor superfamily, and using the X-ray structure of the TNF receptor as a template. The model shows that the interface of the complex is composed of charged residues, with CD40L presenting basic side chains (K143, R203, R207), and CD40 presenting acidic side chains (D84, E114, E117). These residues were studied experimentally through site-directed mutagenesis, and also theoretically using electrostatic calculations with the program Delphi. The mutagenesis data explored the role of the charged residues in both CD40L and CD40 by switching to Ala (K143A, R203A, R207A of CD40L, and E74A, D84A, E114A, E117A of CD40), charge reversal (K143E, R203E, R207E of CD40L, and D84R, E114R, E117R of CD40), mutation to a polar residue (K143N, R207N, R207Q of CD40L, and D84N, E117N of CD40), and for the basic side chains in CD40L, isosteric substitution to a hydrophobic side chain (R203M, R207M). All the charge-reversal mutants and the majority of the Met and Ala substitutions led to loss of binding, suggesting that charged interactions stabilize the complex. This was supported by the Delphi calculations which confirmed that the CD40/CD40L residue pairs E74-R203, D84-R207, and E117-R207 had a net stabilizing effect on the complex. However, the substitution of hydrophilic side chains at several of the positions was tolerated, which suggests that although charged interactions stabilize the complex, charge per se is not crucial at all positions. Finally, we compared the electrostatic surface of TNF/TNFR with CD40L/CD40 and have identified a set of polar interactions surrounded by a wall of hydrophobic residues that appear to be similar but inverted between the two complexes.

Grammer, A. C., et al. (1995). “The CD40 ligand expressed by human B cells costimulates B cell responses.” J Immunol 154(10): 4996-5010. PubMed

The possibility that activated B cells might express a ligand for CD40 that was of functional importance for B cell responses was examined by using highly purified human peripheral blood B cells, as well as a variety of B lymphoblastoid cell lines and hybridomas. Following stimulation with the combination of a calcium ionophore and a phorbol ester, human B cells bound a soluble fusion protein containing the extracellular portion of CD40 and the Fc region of IgG1 (CD40.Ig). A variety of B cell lines and hybridomas also bound CD40.Ig, either constitutively or after activation. In addition, CD40.Ig specifically immunoprecipitated a 33-kDa glycoprotein from surface 125I-labeled activated B cells. The nucleotide sequence of the coding region of the CD40 ligand mRNA amplified by RT-PCR from activated T cells and B cell lines was identical. The CD40 ligand expressed on human B cells was important functionally because homotypic aggregation of CD40 ligand-expressing B cells was inhibited by the CD40.Ig construct. Additionally, RNA and DNA synthesis as well as Ig production by polyclonally activated, highly purified peripheral B cells and a variety of B cell lines were inhibited significantly by the CD40.Ig construct. Finally, B cell lines expressing the CD40 ligand induced Ig production from resting normal B cells in a CD40-dependent manner. These results indicate that human B cells express a ligand for CD40 that is identical with that expressed by activated T cells and that the B cell-expressed CD40 ligand plays an important role in facilitating responses of activated B cells.

Yellin, M. J., et al. (1995). “Functional interactions of T cells with endothelial cells: the role of CD40L-CD40-mediated signals.” J Exp Med 182(6): 1857-1864. PubMed

CD40 is expressed on a variety of cells, including B cells, monocytes, dendritic cells, and fibroblasts. CD40 interacts with CD40L, a 30-33-kD activation-induced CD4+ T cell surface molecule. CD40L-CD40 interactions are known to play key roles in B cell activation and differentiation in vitro and in vivo. We now report that normal human endothelial cells also express CD40 in situ, and CD40L-CD40 interactions induce endothelial cell activation in vitro. Frozen sections from normal spleen, thyroid, skin, muscle, kidney, lung, or umbilical cord were studied for CD40 expression by immunohistochemistry. Endothelial cells from all tissues studied express CD40 in situ. Moreover, human umbilical vein endothelial cells (HUVEC) express CD40 in vitro, and recombinant interferon gamma induces HUVEC CD40 upregulation. CD40 expression on HUVEC is functionally significant because CD40L+ Jurkat T cells or CD40L+ 293 kidney cell transfectants, but not control cells, upregulate HUVEC CD54 (intercellular adhesion molecule-1), CD62E (E-selectin), and CD106 (vascular cell adhesion molecule-1) expression in vitro. Moreover, the kinetics of CD40L-, interleukin 1-, or tumor necrosis factor alpha-induced CD54, CD62E, and CD106 upregulation on HUVEC are similar. Finally, CD40L-CD40 interactions do not induce CD80, CD86, or major histocompatibility complex class II expression on HUVEC in vitro. These results demonstrate that CD40L-CD40 interactions induce endothelial cell activation in vitro. Moreover, they suggest a mechanism by which activated CD4+ T cells may augment inflammatory responses in vivo by upregulating the expression of endothelial cell surface adhesion molecules.