Protective Effect of Carrageenan against Murine Cytomegalovirus Infection in Mice

Abstract

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.