Internal histoincompatability during amphibian metamorphosis?

Larval amphibia are immunologically competent. Yet during metamorphosis, various regressive and progressive processes replace larval with adult structures. These new structures are thought to arise in an immunological environment which provides protection from rejection of non-larval targets. Pre-metamorphic larvae and post-metamorphic adults require carrier-primed amplification in order to generate an anti-hapten response. However, we find that the response to a single challenge of the hapten, TNP, conjugated to a thymus-dependent (TD) carrier, sheep erythrocytes, is substantial in the absence of carrier priming early in metamorphosis. In contrast, the response to TNP on LPS, a thymus-independent carrier, is unaffected by metamorphosis, We suggest that a unique internal histoincompatibility between larval and adult lymphoid cells may provide a substitute for the carrier-priming requirement in the hapten-TD carrier response during metamorphosis.