The ligand for CD40 (CD40L) is a membrane glycoprotein on activated T cells that induces B cell proliferation and immunoglobulin secretion. Abnormalities in the CD40L gene were associated with an X-linked immunodeficiency in humans [hyper-IgM (immunoglobulin M) syndrome]. This disease is characterized by elevated concentrations of serum IgM and decreased amounts of all other isotypes. CD40L complementary DNAs from three of four patients with this syndrome contained distinct point mutations. Recombinant expression of two of the mutant CD40L complementary DNAs resulted in proteins incapable of binding to CD40 and unable to induce proliferation or IgE secretion from normal B cells. Activated T cells from the four affected patients failed to express wild-type CD40L, although their B cells responded normally to wild-type CD40L. Thus, these CD40L defects lead to a T cell abnormality that results in the failure of patient B cells to undergo immunoglobulin class switching.
Interleukin (IL)-1 refers to a group of three polypeptide hormones with a wide range of cellular targets. Two types of IL-1 receptor have been identified and characterized by cDNA cloning. Both human type I and type II IL-1 receptors contain extracellular domains of approximately 310 residues and a single membrane-spanning region. The type I receptor contains a cytoplasmic domain of 213 residues. The cytoplasmic region of the type II receptor is 29 residues in length. It has been found recently that a number of cells express both forms of receptor. By analogy with other cytokine receptor systems, the two IL-1 receptors might be expected to form a heterodimeric complex, the type II receptor being an alpha-chain-like structure, functioning only to bind ligand, and associating with the type I receptor (a beta-chain-like structure) which would transduce signals. In this report we show that this is not the case, but rather that IL-1, when complexed to type II receptor, cannot bind type I receptors, and vice versa. These data show that the complex patterns often observed for IL-1 binding to cells cannot be accounted for by the same type of mechanism that underlies the behavior of, for example, the IL-2 system.
IL-17 is a novel cytokine secreted principally by CD4+ T cells. It has been shown to support the growth of hemopoietic progenitors in vitro; however, its in vivo effects are presently unknown. Adenovirus-mediated gene transfer of the murine IL-17 cDNA targeted to the liver (5 x 10(9) plaque-forming units (PFU) intravenous) resulted in a transiently transgenic phenotype, with dramatic effects on in vivo granulopoiesis. Initially, there was a significant increase (fivefold) in the peripheral white blood count (WBC), including a 10-fold rise in the absolute neutrophil count. This was associated with a doubling in the spleen size over 7-14 days after gene transfer, which returned to near baseline by day 21, although the white blood cell count remained elevated. There was a profound stimulation of splenic hemopoiesis as demonstrated by an increase in total cellularity by 50% 7 days after gene transfer and an increase in hemopoietic colony formation. A maximal increase in frequency of high proliferative potential colonies (HPPC) (11-fold) and CFU-granulocyte-macrophage (GM) and CFU-granulocyte-erythrocyte-megakaryocyte-monocyte (GEMM) (CFU) (6-fold) was seen on day 3 after IL-17 gene transfer. Both CFU and HPPC remained significantly elevated in the spleen throughout day 21, but at reduced levels compared with day 3. Bone marrow CFU and HPPC were elevated on day 3 only by 75% and 25%, respectively, without changes in total cellularity. Thus, murine IL-17 is a cytokine that can stimulate granulopoiesis in vivo. Since IL-17 is principally produced by CD4+ T cells, this cytokine could have therapeutic implications in AIDS-related bone marrow failure and opportunistic infections.
Recombinant human CD40 ligand (hCD40L) was expressed on the surface of CV1/EBNA cells and examined for its ability to induce proliferation and Ig secretion from human B cells in the presence or absence of soluble cytokines. hCD40L was directly mitogenic in a dose-dependent fashion for purified tonsil B cells with maximal proliferation occurring at days 5 to 7. Proliferation induced by CD40L was significantly enhanced in the presence of IL-2, IL-4, or IL-10 and strongly suppressed by transforming growth factor-beta. Although IL-5, TNF-alpha, and IFN-gamma had no stimulatory effect in the presence of hCD40L alone, if IL-4 was also present in cultures, these cytokines enhanced the proliferative response above that seen with IL-4 alone. Interestingly, in the absence of IL-4, IFN gamma had an inhibitory effect on hCD40L-induced proliferation. Although CD40L alone did not enhance Ig secretion, addition of IL-2 or IL-10 to the cultures significantly elevated the levels of IgM, IgG1, and IgA that were observed. Addition of IL-4 to the cultures did not enhance secretion of these isotypes but had a weak inhibitory effect. However, CD40L-mediated induction of IgG4 and IgE was dependent on the presence of IL-4. Of the cytokines examined, only IL-10 enhanced IgE secretion under these conditions. Although transforming growth factor-beta only partially inhibited secretion of IgM, IgG1, and IgA, it was strongly suppressive for IgG4 and IgE production. Our data demonstrate that proliferation and Ig secretion induced in the presence of CD40L can be modulated in a positive and negative fashion by soluble cytokines. IL-2 and IL-10 specifically enhance IgM, IgG1, and IgA production although IL-4, despite costimulating B cell proliferation, does not augment secretion of these isotypes but provided an essential cosignal with CD40L for the production of IgG4 and IgE.
Abstract The tendency of isolated germinal center (GC) B cells to undergo apoptosis was suppressed by recombinant cell‐bound CD40 ligand (CD40L): after 2 days at 37°C, > 80 % of cells remained viable in the presence of CD40L as compared to < 1 % in control cultures. CD40L sustained a high rate of DNA synthesis in GC cells and was more effective than monoclonal antibody to CD40 in this regard. Group I Burkitt lymphoma (BL) cell lines induced to undergo apoptosis with anti‐immunoglobulin or calcium ionophore were also protected by CD40L. In BL cells, this route of rescue was not accompanied by induction of Bcl‐2 protein, the expression of which has been linked to hemopoietic cell survival. Bcl‐2 was induced in GC cells responding to CD40L, but its appearance was a relatively late event not reaching significant levels over controls until day 2 of culture. Thus induction of Bcl‐2 appears to be secondary to the survival signal imparted by CD40L. These findings are discussed in relation to a potential role for CD40L in supporting B cell tumors in vivo and the discovery that the molecular defect in the X‐linked Hyper‐IgM syndrome is targeted to the CD40L gene.
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