PREVALENCE OF CD8(-CELL EXPANSIONS IN RELATION TO AGE IN HEALTHY-INDIVIDUALS() T)

Clonal CD8(+) T-cell expansions have been identified in the peripheral blood of healthy adults and occasionally in children. These expansion s are often large, yet their etiology is unknown. This study evaluated the relationship between age and the prevalence of these expansions i n a healthy population (n = 147) aged 9 months to 85 years. Expansions were determined using immunofluorescence staining with monoclonal ant ibodies to different T-cell receptor (TCR)-variable regions. The overa ll prevalence was 13.6% and increased linearly with age as follows: 0% for 9-month-olds, 2.7% for 4- to 12-year-olds, 13.3% for 20- to 30-ye ar-olds, 20.7% for 35- to 50-year-olds, and 33.4% for 65- to 85-year-o lds. Multiple expansions were observed only in the oldest group. Certa in TCR-variable regions appeared to be preferentially utilized by thes e expansions, which suggests a response to a particular antigenic stim ulus. Childhood illness and vaccination histories did not provide insi ght into the etiology of these expansions. Age was the only measured f actor that was associated with these expansions.