4‐1BB T‐cell antigen binds to mature B cells and macrophages, and costimulates anti‐μ‐primed splenic B cells

Abstract

4-1BB is expressed on activated murine T cells and may function as an accessory signaling molecule during T-cell activation. To identify putative 4-1BB ligands, a fusion protein consisting of the extracellular domain of 4-1BB fused to human placental alkaline phosphatase (4-1BB-AP) was constructed. Alkaline phosphatase activity could then be used as an indicator of the relative amount of bound 4-1BB. These studies indicated that 4-1BB-AP specifically bound to the surface of various mature B and macrophage cell lines. 4-1BB-AP bound at low levels to T cell lines (non-activated and anti-CD3-activated), pre-B-cell lines, and an immature macrophage cell line. 4-1BB-AP did not bind to a glial tumor cell line, HeLa cells, or COS cells. In addition, 4-1BB-AP bound at higher levels to F(ab')2 anti-mu-activated primary B cells compared to anti-CD3-activated primary T cells. Scatchard analysis indicated that the A20 B cell lymphoma expressed 3680 binding sites per cell with a Kd of 1.86 nM. Affinity cross-linking studies demonstrated that a major cell surface species of 120 kDa bound to 4-1BB-AP; 4-1BB-AP also bound to a minor species of approximately 60 kDa. The addition of paraformaldehyde-fixed SF21 cells expressing recombinant 4-1BB synergized with F(ab')2 anti-mu in inducing splenic B cell proliferation suggesting that 4-1BB may function as a regulator of B cell growth.

Regulation of Mouse 4-1BB Expression: Multiple Promoter Usages and a Splice Variant

“…4-1BB binds to a 4-1BB ligand (4-1BBL) expressed by activated antigen-presenting cells (APCs), including monocytes, macrophages, and B cells (Alderson et al, 1994;DeBenedette et al, 1995;Langstein et al, 1998;Pollok et al, 1994). The 4-1BB/4-1BBL interaction provides a costimulatory signal leading to proliferation and differentiation, as well as protection from activation-induced cell death of T cells Kwon et al, 2000;Saoulli et al, 1998;Takahashi et al, 1999).…”

“…The 4-1BB/4-1BBL interaction provides a costimulatory signal leading to proliferation and differentiation, as well as protection from activation-induced cell death of T cells Kwon et al, 2000;Saoulli et al, 1998;Takahashi et al, 1999). The reverse signaling path also exists through 4-1BBL on B cells and dendritic cells resulting in the secretion of immunoglobulins and proinflammatory cytokines, respectively Pollok et al, 1994).…”

Role of 4-1BB:4-1BB ligand in cancer immunotherapy

“…[17][18][19][20] The expression in mice takes several hours following stimulation, slowly increasing and peaking at 60 hours and declining again by 110 hours. 16,19,21 In human, 4-1BB mRNA was detected 1.5 hours after stimulation on T lymphocytes, reaching maximal levels at 8 hours, and declining to background levels by 48 hours. 18 In addition to CD4 þ and CD8 þ T cells, 4-1BB was also expressed on activated natural killer (NK), 22 dendritic cells (DC) 23 as well as neutrophils 24 in mice.…”

“…20 4-1BBL was found to be expressed following stimulation on professional APCs including DCs and macrophages as well as activated B cells in both human and mice. 13,16,21,23,34 Human 4-1BBL message was detected as early as 30 minutes following stimulation through immobilized CD3 monoclonal antibody (mAb) and peaks at 1 hour. 13 4-1BBL was also present at high levels in the sera of some patients with hematological diseases 35 as well as on some carcinoma cell lines.…”

“…50 The engagement of 4-1BBL, in the context of a-IgM providing signal 1, relays costimulatory signals to stimulate B-cell proliferation. 21 Recent studies using transgenic mice expressing 4-1BBL under control of MHC II I-Ea promoter showed that they developed progressive splenomegaly and selective depletion of B220 þ B cells accompanied with low levels of circulating IgG. In addition, these mice exhibited defective humoral responses to Ag challenge suggesting that 4-1BBL may regulate humoral immune responses through the control of the survival of B cell.…”