The effect of localized injection of adjuvant material on the draining lymph node. I. Histology.

The histological accompaniments of adjuvant activity were studied in popliteal nodes of CBA mice at various intervals after footpad injection. Substances tested possessed either extrinsic adjuvanticity but little or no antigenicity (alum, vitamin A alcohol), antigenicity but no extrinsic adjuvanticity (bovine γA-like globulin), both (Freund's complete adjuvant, killed organisms, alum-precipitated BGG), or neither (paraffin oil BP). Substances possessing extrinsic adjuvanticity produced marked persistent enlargement of the draining lymph node, with prominent expansion, hypercellularity and blast transformation in the paracortical areas by the 4th day after injection. This was followed by germinal centre formation and medullary plasmacytosis occurring between the 4th and 10th day. Substances possessing little or no antigenicity produced a feeble germinal centre response and minimal medullary expansion. Bovine γA-like globulin, which lacks extrinsic adjuvanticity, produced a prominent germinal centre and medullary response but a minimal paracortical response. Only mild, transient lymph node enlargement, lasting 1–2 days, was seen after paraffin oil BP. Passive immunization of CBA mice with CBA anti-pertussis hyperimmune serum inhibited the adjuvant action of pertussis, and diminished and delayed the histological changes in the draining lymph node. These data suggested that paracortical expansion and hyperplasia were characteristic histological accompaniments to the injection of substances with extrinsic adjuvanticity. Because paracortical hypercellularity was observed in some instances to precede blast cell transformation, it is suggested that paracortical expansion induced by adjuvants is partly due to an augmented cellular traffic, with a net flux of recirculating lymphocytes into these areas.