L-cystine and l-theanine may contribute to enhancing the immune response against the H1N1 virus.

Abstract

AIM: The immune response to influenza vaccine is attenuated in elderly persons, though they are at greatest risk for morbidity and mortality by influenza virus infection. Experimental studies demonstrate that co-administration of l-cystine and l-theanine enhanced antigen-specific production of immunoglobulin in aged mice infected with influenza virus. We thus investigated the effect of l-cystine and l-theanine on antibody induction by influenza vaccines in elderly persons. METHODS: Residents in a nursing home were randomly allocated to l-cystine and l-theanine (n = 32) or placebo (n = 33). The test substances were administered p.o. for 14 days before immunization. Serum influenza virus antibody titers were measured before and 4 weeks after vaccination. RESULTS: Vaccination significantly elevated hemagglutination inhibition (HI) titers for all the three strains of influenza viruses (A/New Caledonia [H1N1], A/New York [H3N2] and B/Shanghai) in both groups. HI titers after vaccination were not significantly different between the two groups for either strain. Also, the seroconversion rate was not significantly different between the two groups in the aggregate. A stratified analysis showed that the rate of seroconversion was significantly greater in the l-cystine and l-theanine group compared with the placebo group for influenza virus A (H1N1) among subjects with low serum total protein (63% vs 10%, P < 0.05) or low hemoglobin (71% vs 9%, P < 0.05). CONCLUSION: Co-administration of l-cystine and l-theanine before vaccination may enhance the immune response to influenza vaccine in elderly subjects with low serum total protein or hemoglobin.