Low-dose exposure to antigen induces sub-clinical sensitization

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Abstract
We examined the effects of a small initial sensitizing dose of antigen (dinitrochlorobenzene, DNCB) on the subsequent response to a second, defined sensitizing stimulus. The second stimulus was actually the regimen of four doses of DNCB (3.125, 6.25, 12.5, and 25 .mu.g; total 46.9 .mu.g) normally used as the elicitation challenge. In two separate experiments 13 and 18 control subjects received an initial ''challenge'' with the four doses to induce sensitivity, and 4 weeks later their responses were determined with a second, elicitation challenge. Two groups of 12 and 15 experimental subjects received an initial dose predicted to induce clinically detectable sensitivity in 50% or 25%, respectively. Four weeks later, their responsiveness was determined with qualitative challenge and the subjects who gave no response received a further challenge 4 weeks later. Their responses, compared with those from the control subjects, were augmented, indicating that sub-clinical priming of the immune system had indeed occurred.