Regulation of Carrier‐Specific Response via a Haptenic Epitope

Influences of haptenic epitopes on the regulation ofcarrier‐specific responses are of importance in vaccination and heterogenization protocols. This situation was modelled by analysing the primary and secondary anti‐horse red blood cell (HRBC) response under the influence of a haptenic epilope (trinitrophenol. TNP). Primary and secondary anti‐HRBC responses were diminished in the presence of TNP. The primary response against the carrier was delayed in the presence of TNP and primary and secondary anti‐carrier responses vanished more rapidly in response to TNP‐HRBC than in response to HRBC. When frequencies of HRBC‐specific B cells were determined under limiting dilution (LD) conditions, a lower frequency of HRBC‐speeific B cells was discovered in the presence of TNP‐HRBC as compared lo HRBC. Accordingly, after priming with HRBC, the frequency of B cells was increased by a factor of 49, while after priming with TNP‐HRBC the frequency was only increased by a factor of 11. Furthermore, haptenic epitopes influenced the anti‐carrier response via regulatory elements. Under physiological conditions, hapten‐specific help was insufficient and hapten‐specific B cells competed for earrier‐specific helper T cells (TH). Suppression was more efficient in hapten‐carrier‐primed mice than in carrier‐primed mice and in line with this observation, an increased frequency of suppressor T cells (Ts) was observed in LD cultures when TNP‐HRBC instead of HRBC were used as antigen. It is concluded that haptenic epitopes are relevant for the anti‐carrier response, since hapten‐specific B cells competc for carrier‐specific help, hapten‐specific suppression down‐regulates carrier‐specific help, and the hapten may hide immunogenie epitopes of the carrier, resulting in incomplete activation of the B‐cell repertoire.