Humoral bactericidal systems: antibacterial potential of serum from young animals.

The antibacterial potential of fresh serum obtained from young animals during a pre-antibody period of development was assessed against two smooth and two rough strains of gram-negative bacteria. The bactericidal capacity of serum from 3- to 4-week-old guinea pigs and 4- to 5-week-old rabbits was compared with that of serum from adults. Serum from young animals was deficient in natural antibodies, and in conventional dilution assays the bactericidal action was unimpressive, especially against the smooth strains. However, when decimal increments of bacteria were incubated in fresh undiluted serum, killing of both smooth and rough strains proved substantial. This finding may have particular meaning in the very young animal when natural antibodies are at ebb: cellular defense mechanisms may function less efficiently at this time and effect a greater reliance on humoral antibacterial systems.