Biological function and distribution of human interleukin‐12 receptor β chain

Abstract

We previously described the cloning of a cDNA encoding an interleukin-12 receptor (IL-12R) subunit, designated beta, that bound IL-12 with low affinity when expressed in COS cells. We now report that a pair of monoclonal antibodies (mAb), 2B10 and 2.4E6, directed against different epitopes on the IL-12R beta chain, when used in combination, strongly inhibited IL-12-induced proliferation of activated T cells, IL-12-induced secretion of interferon-gamma by resting peripheral blood mononuclear cells (PBMC), and IL-12-mediated lymphokine-activated killer cell activation. The mAb had no effect on lymphoblast proliferation induced by IL-2, -4, or -7. Thus, the IL-12R beta chain appears to be an essential component of the functional IL-12R on both T and natural killer (NK) cells. We previously observed that high affinity IL-12R were expressed on activated T and NK cells, but not B cells. Studies using flow cytometry and reverse transcription-polymerase chain reaction analysis showed that IL-12R beta chain was expressed on several human T, NK, and (surprisingly) B cell lines, but not on non-lymphohematopoietic cell lines. The Kit225/K6 (T cell) and SKW6.4 (B cell) lines were found to express the greatest amounts of IL-12R beta chain (800-2500 sites/cell); however, Kit225/K6 but not SKW6.4 cells bound IL-12. Similar to SKW6.4 B cells, activated tonsillar B lymphocytes expressed IL-12R beta chain but, consistent with previous results, did not display detectable IL-12 binding. Likewise, up to 72% of resting PBMC from normal volunteer donors expressed IL-12R beta, but did not bind measurable amounts of IL-12. These results indicate that expression of IL-12R beta is essential, but not sufficient, for expression of functional IL-12R. We speculate that expression of functional, high-affinity IL-12R may require the presence of a second subunit that is more restricted in its expression than IL-12R beta.

Interleukin-12 Is Synthesized by Mesangial Cells and Stimulates Platelet-Activating Factor Synthesis, Cytoskeletal Reorganization, and Cell Shape Change

“…46,47 Herein, we demonstrate that cultured MCs bind IL-12 and express the human low-affinity IL-12 ␤1 chain receptor under basal conditions. A similar expression of the low-affinity IL-12 receptor ␤1 chain has been observed in unstimulated T lymphocytes, 45 in which IL-12, even in the absence of the ␤2 subunit, induces an efficient production of interferon-␥ 12 and in neutrophils, in which IL-12 stimulates the synthesis of PAF. 11 We observed that IL-12 induces a dose-dependent synthesis of PAF also by MCs.…”

“…The functional high-affinity IL-12 receptor is composed of two ␤-type cytokine receptor subunits, each independently exhibiting a low-affinity binding for IL-12. Whereas the ␤1 subunit is expressed in basal conditions on lymphocytes, 45 the distribution of the ␤2 subunit is more restricted, and its expression appears to be related to lymphocyte activation or differentiation. 46,47 Herein, we demonstrate that cultured MCs bind IL-12 and express the human low-affinity IL-12 ␤1 chain receptor under basal conditions.…”

IL-12 Receptor β2 (IL-12Rβ2)-Deficient Mice Are Defective in IL-12-Mediated Signaling Despite the Presence of High Affinity IL-12 Binding Sites

“…Blocking of IL-12 binding to IL-12R␤1 by using an anti-IL-12R␤1 Ab (28) or IL-12p40 homodimer, a known IL-12 receptor antagonist, abrogates the biological activities induced by IL-12 (29). Likewise, Con A-activated splenocytes from IL-12R␤1 Ϫ/Ϫ mice fail to proliferate, produce IFN-␥, or generate Th1 cells in response to IL-12 (7).…”

CD47 Ligation Selectively Inhibits the Development of Human Naive T Cells into Th1 Effectors

“…6). IL-12R␤1 is constitutively expressed on several types of cells, including resting T and B cells, which are not responsive to IL-12 (7). The coexpression of these two chains is required for IL-12 responsiveness and Th1 cell development.…”