Intraperitoneal inoculation with live influenza A virus confers protection against intranasal infections in mice and ferrets. However, the responses of peritoneal cells to influenza A virus have not been investigated. Here we show that intraperitoneal inoculation with A/WSN/1933 (H1N1) virus induced virus-reactive IgG production in the peritoneal cavity in mice. The infection resulted in substantial but transient B cell and macrophage depletion along with massive neutrophil infiltration, but virus growth was not detected. Influenza A viruses bound to α-2,6-linked sialic acids of B cells and macrophages and induced apoptotic death of peritoneal cavity cells. However, re-infection with A/WSN/1933 virus did not have adverse effects on immune cells most likely because of the neutralizing antibodies produced in response to the first exposure. Infection of BALB/c mice with A/WSN/1933 induced cross-protection against an otherwise lethal intraperitoneal dose of A/Hongkong/4801/2014 (H3N2) virus. This information suggests that immunological responses in the peritoneal cavity can induce effective defense against future virus infection. Considering the unexpected potent immunoregulatory activity of the peritoneal cells against influenza viruses, we suggest that comparative studies on various immune reactions after infection through different routes may contribute to better selection of vaccination routes in development of efficacious influenza vaccines.

Transmembrane 4 superfamily member 5 protein (TM4SF5) is a potential therapeutic target for hepatocellular carcinoma (HCC) and colon cancer. In a previous study, we demonstrated the prophylactic and therapeutic effects of a TM4SF5-specific peptide vaccine and monoclonal antibody in HCC and colon cancer in a mouse model. Here, we designed a cyclic peptide targeting TM4SF5. Cyclic peptide-specific antibodies were produced in mice after immunization with a complex of the peptide, CpG-DNA, and liposomes. Intravenous injection of the CT-26 mouse colon cancer cell line into mice induced tumors in the lung. Immunization with the peptide vaccine improved the survival rate and reduced the growth of lung tumors. We established a monoclonal antibody specific to the cyclic TM4SF5-based peptide and humanized the antibody sequence by complementarity determining region-grafting. The humanized antibody was reactive to the cyclic peptide and TM4SF5 protein. Treatment of CT-26 cells with the humanized antibody reduced cell motility in vitro. Furthermore, direct injection of the humanized anti-TM4SF5 antibody in vivo reduced growth of lung tumors in mouse metastasis model. Therefore, we conclude that the immunization with the cyclic peptide vaccine and injection of the TM4SF5-specifc humanized antibody have an anti-metastatic effect against colon cancer in mice. Importantly, the humanized antibody may serve as a starting platform for further development and application in clinical settings.

CpG-DNA activates various immune cells, contributing to the host defense against bacteria. Here, we examined the biological function of CpG-DNA in the production of bacteria-reactive antibodies. The administration of CpG-DNA increased survival in mice following infection with methicillin-resistant S. aureus and protected immune cell populations in the peritoneal cavity, bone marrow, and spleen. CpG-DNA injection likewise increased bacteria-reactive antibodies in the mouse peritoneal fluid and serum, which was dependent on TLR9. B cells isolated from the peritoneal cavity produced bacteria-reactive antibodies in vitro following CpG-DNA administration that enhanced the phagocytic activity of the peritoneal cells. The bacteria-reactive monoclonal antibody enhanced phagocytosis in vitro and protected mice after S. aureus infection. Therefore, we suggest that CpG-DNA enhances the antibacterial activity of the immune system by protecting immune cells and triggering the production of bacteria-reactive antibodies. Consequently, we believe that monoclonal antibodies could aid in the treatment of antibiotic-resistant bacterial infections.

No abstract

CpG-DNA activates the host immune system to resist bacterial infections. In this study, we examined the protective effect of CpG-DNA in mice against Escherichia coli (E. coli) K1 infection. Administration of CpG-DNA increased the survival of mice after E. coli K1 infection, which reduces the numbers of bacteria in the organs. Pre-injection of mice with CpG-DNA before E. coli K1 infection increased the levels of the complement C3 but not C3a and C3b. The survival of the mice after E. coli K1 infection was significantly decreased when the mice were pre-injected with the cobra venom factor (CVF) removing the complement compared to the non-CVF-treated mice group. It suggests that the complement has protective roles against E. coli K1 infection. In addition, the survival of complement-depleted mice was increased by CpG-DNA pre-administration before E. coli K1 infection. Therefore, we suggest that CpG-DNA enhances the anti-bacterial activity of the immune system by augmenting the levels of complement systems after E. coli K1 infection and triggering other factors as well. Further studies are required to investigate the functional roles of the CpG-DNA-induced complement regulation and other factors against urgent bacterial infection.