An age-old paradigm challenged: old baboons generate vigorous humoral immune responses to LcrV, a plague antigen.

Immune senescence in the elderly results in decreased immunity with a concomitant increase in susceptibility to infection and diminished efficacy of vaccination. Nonhuman primate models have proven critical for testing of vaccines and therapeutics in the general population, but a model using old animals has not been established. Toward that end, immunity to LcrV, a protective Ag from Yersinia pestis, was tested in young and old baboons. Surprisingly, there was no age-associated loss in immune competence; LcrV elicited high-titer, protective Ab responses in the older individuals. The primary responses in the younger baboons were lower, but they did show boosting upon secondary immunization to the levels achieved in the old animals. The LcrV Ag was also tested in mice and, as expected, age-associated loss of immunity was seen; older animals responded with lower-titer Abs and, as a result, were more susceptible to Yersinia challenge. Thus, although age-related loss in immune function has been observed in humans, rodents, and some nonhuman primates, baboons appear to be unusual; they age without losing immune competence.