Abstract: Objective To observe the influence of Mycobacterium vaccae on the humoral immunity of the PPD positive case.Methods The serum antibodies to IgG of the PPD positive cases were measured before and after Mycobacterium vaccae being injected(12weeks).The serum antibodies of another group were also measured before and after taking 6 months INH.The OD value of them was compared.Result At the 12 weeks after injecting Mycobacterium vaccae the OD value of IgG is higher than that before ( P<0.01) .The positive rate is from 25%to 80%.While those who taking INH have no change.Conclusion The increasing of IgG after M.vaccae injection shows that it can boost human beings humoral immunity.It may be better to prevent tuberculosis than that of taking medicine.

Key words: Mycobacterium vaccae, IgG, PPD