The Effect of Killed Influenza Virus Vaccine on the Kinetics of Normal Human Lymphocytes

Inoculation of humans with wild or attenuated myxoviruses induces transient alterations in lymphocyte count and function. The effects of A/New Jersey/76 virus, a killed influenza virus vaccine, on circulating lymphocyte subpopulations were evaluated in 25 volunteers. Thymus-dependent (T) and independent (B) lymphocytopenias occurred 24 hr after vaccination. T lymphocytopenia was universal, profound (65% drop; P less than 0.001), and long-lived (greater than nine days). B lymphocytopenia was observed in 18 individuals, was moderate (39% drop]; P less than 0.001), and short-lived (less than three days). Null-cell counts rose concurrently, peaked three days after vaccination (188% rise P less than 0.001), and returned to prevaccination levels by day 28. Cell exposure to thymosin in vitro increased T-cell levels proportionately to the degree of null lymphocytosis (peaking three days after vaccination [45% conversion of null cells to T cells; P less than 0.001]), suggesting that postvaccination null cells might be emergent precursor T cells compensating for T lymphocytopenia. Seroconversion occurred in 90% of the volunteers by day 28, suggesting preserved effector B- and helper T-cell functions despite the marked changes in lymphocyte subpopulations.