Using the leucocyte-migration test, cell-mediated immunity to hepatitis-B antigen (HBAg) was found in 12 (86%) of the 14 members of a liver-unit staff whose work involved frequent contact with purified antigen. In addition, 5 (36%) of them had hepatitis-B antibody (HBAb) detected by radioimmunoassay. Findings in the other 29 staff members were not significantly different from those in 43 age and sex matched factory-worker controls. 30% of the controls had evidence of cell-mediated immunity and 7% had HBAb. 6 patients recovering from acute HBAg-positive hepatitis also had both cell-mediated immunity and HBAb. However, only 1 of the 86 staff members and factory controls tested had ever had clinical hepatitis and liver-function tests were normal. It is suggested that frequent exposure to low-dose HBAg by the oral route may result in a primary immunological response in the gastrointestinal mucosa without viræmia or liver disease and that such immunity is likely to be protective.
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