Analysis of immunological effects of a non-specific immunostimulator, germanium biotite

Abstract

Germanium biotite, a natural mineral within the mica group, is comprised of mainly silicate. It has been reported that use of this mineral as feed supplement could stimulate a non-specific immune system. The aims of the present study were to demonstrate the mechanism of the immune enhancing effects in vitro and to evaluate the immune stimulating effects of germanium biotite in cattle and pigs as an initial step towards the development of alternative feed supplement for prevention of diseases in livestock industry. To demonstrate the mechanism of immune enhancing of germanium biotite, murine macrophage cell line, RAW 264.7, were treated with 100 µg/mL mica (germanium biotite) and changes in global gene expression upon mica treatment for 12 and 48 h were determined using microarrays. To evaluate the immune enhancing effects in vivo, the prophylactic effects of germanium biotite against respiratory diseases in cattle were investigated using challenge experiment with bovine herpesvirus type 1 (BHV- 1) and Mannheimia haemolytica serotype A1. The effects of the non-specific immune stimulator germanium biotite on foot-and-mouth disease (FMD) vaccination and immune system in cattle were also analyzed. In addition, the investigation of immune responses to FMD virus (FMDV) challenge in FMD vaccinated mini-pigs after oral administration of the germanium biotite was carried out using Andong strain. Following the mica treatment, RAW 264.7 cells showed a change in an expression level of 1,128 genes after 48 h treatment. Specifically, genes associated with the cell cycle, DNA replication, and pyrimidine and purine metabolisms, were down-regulated in cells treated with mica. Mica treatment also up-regulated genes associated with lysosome and phagosome function, which are both required for macrophage activities. These results indicate that mica, major component of the germanium biotite, could activate macrophages, in part, through up-regulation of these pathways. In challenge experiment of bovine respiratory diseases (BRDs), germanium biotite-fed group showed a lower cumulative clinical score (CCS) than the control group. In accordance with this clinical result, enhanced clearance of BHV-1, a low level of bacteria shedding, tempered superficial lesions, and moderated histopathological signs were observed in the germanium biotite-fed group, compared to the control group. These results indicate that germanium biotite has prophylactic effects against BRDs and could be a candidate for a new alternative feed supplement in cattle, through its effects as a non-specific immune stimulator. In experiment of FMD vaccination and immune responses in cattle, it was found that high levels of IgG and IgA titers in serum and saliva were longstanding in the germanium biotite-fed group, compared to the control. Generally, higher virus-neutralizing antibody titers were observed in the germanium biotite-fed group. After feeding germanium biotite, subpopulation of the CD4+ and major histocompatibility complex (MHC) class II+ of lymphocytes and levels of interferon (IFN)-γ, interleukin (IL)-1α, IL-1β, and IL-4 gene expression were significantly increased in the feeding group. Feeding with germanium biotite increased lymphocyte proliferation at 23 weeks and lysozyme activity at 8 weeks after feeding. These results suggest that germanium biotite feeding could increase the protection against FMD virus infection via the induction of higher humoral and cellular immune responses in cattle. Following the FMDV challenge, the germanium biotite-fed pigs showed high levels of IL-8 in serum, and increased cellular immune responses to stimulation with the Andong strain antigen compared to pigs of the control group. In addition, higher FMDV neutralizing antibody titers were detected in the germanium biotite-fed group than in the control group before the challenge. The findings of this study indicate that germanium biotite supplement might enhance immune responses to the FMD vaccine and FMDV challenge in pigs. Taken together, germanium biotite oral administration showed enhancing the immune responses to challenge of BHV-1 and Mannheimia haemolytica serotype A1, FMD vaccination, and FMDV challenge. These immune enhancing effects may be related to its ability to activate non-specific immunity. It is also presumed that this enhanced non-specific immunity could be associated with, in part, macrophage activation by germanium biotite such as up-regulation in lysosome and phagosome pathways. Hence, germanium biotite could be a candidate for new alternative feed supplement to reinforce immunity, thereby reducing the risk of diseases outbreak in livestock industry.