Mechanism of anticancer host response induced by OK-432, a streptococcal preparation, mediated by phagocytosis and Toll-like receptor 4 signaling.
It has previously been reported by our group that Toll-like receptor (TLR) 4 is involved in anticancer immunity induced by OK-432, a Streptococcus-derived immunotherapeutic agent. However the detailed mechanism of the OK-432-induced immune response via TLR4 remained uncertain, because it may not be possible for OK-432, which consists of whole bacterial bodies, to bind directly to TLR4. In the current study, we conducted in vitro and in vivo experiments to investigate the hypothesis that OK-432 may first be captured and dissolved by phagocytes and that the active components released by the cells may then induce host responses via TLR4. TS-2 monoclonal antibody, which recognizes an active component of OK-432 designated OK-PSA was used in the current study. First, it was observed that OK-432-induced cytokine production by dendritic cells (DCs) and macrophages was significantly inhibited in vitro by cytochalasin B, a phagocytosis inhibitor. Immunofluorescence staining using TS-2 demonstrated that OK-432 was captured and dissolved by phagocytes. OK-PSA was detected in the supernatants derived from OK-432-treated DC culture by enzyme-linked immunosorbent assay using TS-2. Supernatants from OK-432-treated DC culture increased nuclear factor (NF)-kappaB activity in TLR4-expressing cells, and the increased activity was inhibited by TS-2 antibody. OK-432 itself did not activate NF-kappaB in these cells. In in vivo experiments, the anticancer effect of OK-432 was significantly inhibited by suppression of phagocytosis activity by cytochalasin B. In this case, the amount of OK-PSA, an active component of OK-432, in the sera was also reduced by cytochalasin B. These findings elucidated the mechanism mediated by phagocytosis and TLR4 signaling in the immune effect of OK-432.
Okamoto
Masato
M
Second Department of Oral and Maxillofacial Surgery, Tokushima University School of Dentistry, Tokushima, Japan. mokamoto@dent.tokushima-u.ac.jp
Oshikawa
Tetsuya
T
Tano
Tomoyuki
T
Ahmed
Sharif Uddin
SU
Kan
Shin
S
Sasai
Akiko
A
Akashi
Sachiko
S
Miyake
Kensuke
K
Moriya
Yoichiro
Y
Ryoma
Yoshiki
Y
Saito
Motoo
M
Sato
Mitsunobu
M
D000276:Adjuvants, Immunologic; D000818:Animals; D003713:Dendritic Cells / Q000276:immunology; D005260:Female; D006801:Humans; D017737:Macrophages, Peritoneal / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D009369:Neoplasms / Q000276:immunology*; D010587:Phagocytosis / Q000276:immunology*; D010844:Picibanil / Q000276:immunology* / Q000378:metabolism; D015398:Signal Transduction / Q000276:immunology*; D051197:Toll-Like Receptor 4 / Q000276:immunology*
D000276:Adjuvants, Immunologic; D051197:Toll-Like Receptor 4; D010844:Picibanil