Host-mediated antiviral activity of Lactobacillus casei against cytomegalovirus infection in mice

Protective Effect of Carrageenan against Murine Cytomegalovirus Infection in Mice

The protective effect of iota-carrageenan (CAR) was evaluated against murine cytomegalovirus (MCMV) infection in mice. Female ICR mice were challenged intraperitoneally (i.p.) with 3 LD50 of salivary gland-passaged MCMV. More than 0.5 mg of CAR showed a protective effect on mice only when CAR was administered i.p. and then MCMV was inoculated i.p. The protective effect of CAR was evidenced by an increase in plaque-forming unit per LD50 and a decrease in the titre of infectious viruses in the target organs. Neither a virucidal nor a virustatic effect on MCMV was evidenced for CAR. The protective effect of CAR seemed to be host-mediated.

Pretreatment of mice with CAR augmented natural killer (NK) activity of the spleen cells without elevating the serum interferon level. However, administration of anti-asialo GM1 antibody did not nullify the inhibitory effect of CAR on virus replication in the target organs. MCMV infection induced leukopenia including neutropenia and lymphopenia in saline-treated mice. Pretreatment with CAR protected mice from those signs, except for slight lymphopenia. Administration of cyclophosphamide induced severe leukopenia including neutropenia and lymphopenia even in CAR-treated mice. Under such conditions, the protective effect of CAR against MCMV infection was abrogated by cyclophosphamide. Thus, the protective effect of CAR seems to be non-NK-mediated.

Dietary probiotic supplementation enhances natural killer cell activity in the elderly: an investigation of age-related immunological changes

Many elderly subjects are at increased risk of infectious and noninfectious diseases due to an age-related decline in lymphoid cell activity (immunosenescence). Noninvasive means of enhancing cellular immunity are therefore desirable in the elderly. Previous reports have suggested that dietary supplementation could represent an effective means of enhancing the activity of circulating natural killer (NK) cells in the elderly. In the present study, we have conducted a pre-post intervention trial to determine the impact of dietary supplementation with probiotic lactic acid bacteria (LAB) on peripheral blood NK cell activity in healthy elderly subjects. Twenty-seven volunteers consumed low-fat/low-lactose milk supplemented with known immunostimulatory LAB strains (Lactobacillus rhamnosus HN001 or Bifidobacterium lactis HN019) for a period of 3 weeks. A dietary run-in of milk alone was shown to have no significant effect on NK cells. In contrast, the proportion of CD56-positive lymphocytes in peripheral circulation was higher following consumption of either LAB strain, and ex vivo PBMC tumoricidal activity against K562 cells was also increased. Supplementation with HN001 or HN019 increased tumoricidal activity by an average of 101 and 62%, respectively; these increases were significantly correlated with age, with subjects older than 70 years experiencing significantly greater improvements than those under 70 years. These results demonstrate that dietary consumption of probiotic LAB in a milk-based diet may offer benefit to elderly consumers to combat some of the deleterious effects of immunosenescence on cellular immunity.

Induction of resistance in mice against murine cytomegalovirus by cellular components of Lactobacillus casei

Recently, we reported that heat-killed Lactobacillus casei (LC) protected mice from murine cytomegalovirus (MCMV) infection by augmentation of natural killer (NK) cell activity. In the present study, we examined which components of LC cell induce the nonspecific resistance most effectively. Whole cell preparation of original LC, susceptible to bacteriophages SG-T and J1, was more effective than its mutants resistant to either bacteriophage. Although the activity of LC cells decreased upon fractionation, cell wall fractions were more active than cytoplasmic fractions. Glycoprotein (GP), a cell wall constituent, was a potent inducer of the resistance. The relative activity of cellular components to induce the resistance was evaluated by a protection index, a ratio of plaque-forming units (PFU) per 50% lethal dose (LD50) for treated mice to that for untreated mice. The protection indices of LC cells and GP were approximately 80 and 28, respectively. The protective effect of GP was evidenced by a decrease in titers of infectious viruses replicated in the target organs. Not only LC cells but also GP, although to a lesser degree, enhanced NK cell activity both in uninfected mice and MCMV-infected mice. The activity of LC cells and GP to augment NK cell activity correlated with the protection index. GP treatment did not modify interferon (IFN) production during MCMV infection. Thus, GP of LC cells seems to be the active principle to endow mice with resistance to MCMV.

Susceptibility of W/WV mice to murine cytomegalovirus infection

The susceptibility of congenitally anemic W/WV mice to infection with murine cytomegalovirus (MCMV) was examined. W/WV mice showed a higher mortality rate and shorter survival time after MCMV infection than did their +/+ littermate mice. In addition, W/WV mice showed a lower plaque-forming unit (PFU) per 50% lethal dose (LD50) and produced higher titers of infectious virus in various organs. The mortality rate and survival time of W/WV mice which received a bone marrow graft 4 weeks before infection was completely restored to the level for +/+ mice, suggesting the importance of the cells of myeloid origin. Although natural killer (NK) activity of W/WV mice was comparable to that of +/+ mice before infection, marked reduction was observed after MCMV infection. Furthermore, OK-432 treatment failed to enhance NK activity of W/WV mice. Impaired NK response was also completely restored by bone marrow grafting 4 weeks before infection. The level of serum interferon (IFN) of infected or uninfected W/WV mice was comparable to that of +/+ mice. Therefore, impaired NK inducibility seems to be responsible, at least in part, for the high susceptibility of W/WV mice to MCMV infection.