Effect of age on antibody responses after lung immunization.

The effects of age on the number of lymphoid cells producing specific IgM antibody (AFC) and the level of specific IgM, IgG, and IgA antibody after lung immunization were evaluated in groups of dogs 2 through 16 yr of age. A trend for lowered antibody responses in blood was observed with increasing age, and significantly lowered antibody responses were measured in lavage fluids from immunized lung lobes of older dogs. Statistical evaluations indicated that the lowered antibody responses in the lung were due in part to the reduced AFC and level of specific antibody in the blood. However, a less intense inflammatory response to antigen instilled into the lungs of older dogs also significantly contributed to the lowered antibody responses in their lungs. Additional studies are needed to determine if the loss of inflammation and antibody responses in the lungs of aged dogs increases their susceptibility to pulmonary infections.