Anti-MRC1 monoclonal antibody, clone MR5D3 [R-PE]

BackgroundAndrogen deprivation results in massive apoptosis in the prostate gland. Macrophages are actively engaged in phagocytosing epithelial cell corpses. However, it is unknown whether microtubule-associated protein 1 light chain 3 alpha (LC3)-associated phagocytosis (LAP) is involved and contribute to prevent inflammation. MethodsFlow cytometry, RT-PCR and immunohistochemistry were used to characterize the macrophage subpopulation residing in the epithelial layer of the rat ventral prostate (VP) after castration. Stereology was employed to determine variations in the number of ED1 and ED2. Mice were treated with either chloroquine or L-asparagine to block autophagy. ResultsM1 (iNOS-positive) and M2 macrophages (MRC1+ and ARG1+) were not found in the epithelium at day 5 after castration. The percentage of CD68(+) (ED1) and CD163(+)(ED2) phenotypes increased after castration but only CD68(+) cells were present in the epithelium. RT-PCR showed increased content of the autophagy markers Bcl1 and LC3 after castration. In addition, immunohistochemistry showed the presence of LC3(+) and ATG5(+) cells in the epithelium. Double immunohistochemistry showed these cells to be CD68(+)/LC3(+), compatible with the LAP phenotype. LC3(+) cells accumulate significantly after castration. Chloroquine and L-asparagine administration caused inflammation of the glands at day 5 after castration. ConclusionsCD68(+) macrophages phagocytose apoptotic cell corpses and activate the LAP pathway, thereby contributing to the preservation of a non-inflammed microenvironment. Marked inflammation was detected when autophagy blockers were administered to castrated animals.

Tumor-associated macrophages (TAM) are a major component of tumor stroma. It has been reported that TAMs have M2-like phenotype and facilitate tumor progression by promoting angiogenesis and immunosuppression. Melittin, a major polypeptide of bee venom, has been widely studied as an anti-cancer drug due to its cytotoxicity to malignant cells. However, very little is known regarding the effect of melittin on immune cells in the tumor microenvironment. This study focuses on the effect of melittin on TAMs in a Lewis lung carcinoma mouse model. Melittin inhibited the rapid tumor growth compared to the control in vivo. Melittin increased the M1/M2 ratio of TAMs by selectively reducing the number of CD206(+) M2-like TAMs while not altering the population of CD86(+) M1-like TAMs. Melittin also preferentially binds to M2 macrophages, and this binding was not associated with phagocytosis. Gene and protein expression of vascular endothelial growth factor (Vegf) and mannose receptor C type 1 (Mrc1/CD206) was reduced in M2-like bone marrow-derived macrophages by melittin treatment, but there was no significant change in the gene level of Vegf and FMS-like tyrosine kinase 1 (Flt1/VEGFR1) in tumor cells in vitro.Additionally, the levels of VEGF and CD31, markers of angiogenesis, were significantly decreased by melittin treatment in tumor tissues. This study revealed a novel role for melittin in tumor treatment and suggested that melittin could be a promising therapeutic agent for targeting M2-like TAMs.