In this experiment, we proved the efficacy of the BIFN-transformed B. longum cells on the CVB3-induced myocarditis. Oral administration of IFN-transformed B. longum cells can reduce significantly the cardiac inflammatory area of CVB3-infected mice by day 14 compared with the B and saline groups respectively, which suggested that BIFN-transformed B. longum cells can improve the severity of disease. It has been demonstrated that the dominant pathogenic process in the early stages of CVB3 infection is the direct attack on myocardial cells by the virus, therefore antivirus treatment at this phase is very important to improve the development of virus infection . Our data indicated that the cardiac virus titers in the murine heart of BIFN group were decreased significantly compared with B group, which indicated that this recombinant B. longum may improve cardiac inflammation partly by inhibition of virus replication at the early stage of CVB3 infection. Classical theories suggest that CD4+ Th1 cells play a vital role against virus infection in adaptive immune responses by production of IFN-γ for effective clearance of virus invasion. In this study, IFN-transformed B. longum increased the expression of Th1 cytokines (IFN-γ and TNF-α) mRNA in cardiac tissue and enhanced the secretion of Th1 cytokines (IFN-γ and TNF-α) from splenocytes, which suggested that this recombinant B. longum is able to induce expression of CD4+ Th1 cells against virus infection.
Our former studies have shown that hIFN-α2b from IFN-transformed B. longum is expressed mainly as a mature secretory cytokine and that serum hIFN-α2b level can be enhanced in the mice that have been administrated orally with B. longum [12, 13]. As we know, the expression of hIFN-α2b in IFN-transformed B. longum is mainly induced by L-arabinose, which is a component of biopolymers such as hemicellulose and pectin . The administration of IFN-transformed B. longum has been demonstrated to increase the serum and intestinal IFN-α2b level and we hypothesize that IFN expression by this bifidobacteria in mice might be induced persistently by L-arabinose in MRS or by the administered food and then enter the blood circulation by gastrointestinal absorption . In this study, we compared mice either treated with saline and control B. longum mice respectively. The Mx1 mRNA levels, which represent the local tissue IFN concentration, were increased significantly in cardiac tissues in the BIFN group, which suggested that IFN-transformed B. longum can increase the level of active type 1 IFN locally. Further study is needed to ascertain how to control the expression of IFN stably in gut and whether these bacteria affect the microbial flora.
Bifidobacterium has many beneficial effects on human health that include prevention of infection, immunomodulation, promotion of lactose digestion and protection against colon cancer [9–11]. Recently, genetically engineered Bifidobacterium has been used successfully as an exogenous gene delivery carrier for bowel disease and cancer gene therapy [9–11, 27]. This finding suggests that Bifidobacterium may be a suitable carrier for human gene expression and secretion in the intestinal tract for the treatment of gastrointestinal diseases. Here, we demonstrated the efficacy of BIFN-transformed B. longum to CVB3-induced myocarditis in the mice. Our data showed, compared with IFN-transformed B. longum, that IFN-α2b administered intramuscularly could reduce significantly virus infection, decrease the severity of virus-induced myocarditis, and induce a robust Th1 pattern in the spleen and heart. Nevertheless, IFN-transformed B. longum has its own advantages that include localization in the gastrointestinal cavity and spread of the physiological role locally . Further experimentation is needed to evaluate whether IFN-transformed B. longum can be added to probiotic yogurt or diet and whether it can protect high-risk people who eat these products from the virus myocarditis. The model in this study was to inoculate with CVB3 intraperitoneally and this route may affect the therapeutic efficacy of IFN-transformed B. longum compared with IFN-α2b given intramuscularly. The preventive or therapeutic roles of IFN-transformed B. longum in virus diseases need to be studied further.
In conclusion, oral administration of IFN-transformed B. longum can decrease the severity of virus-induced myocarditis, reduce the virus titers in the heart and induce a Th1 pattern in the spleen and heart in vivo. IFN-transformed B. longum may play a potential role in the treatment of coxsackie virus B3-induced myocarditis. However, the advantages of the IFN-transformed B. longum in the treatment and prevention of enterovirus infection need to be studied further.