DETECTION AND LOCALIZATION OF 3,3',4,4'-TETRACHLOROBIPHENYL-INDUCED P4501A PROTEIN IN AVIAN PRIMARY IMMUNE TISSUES

P4501A can be detected in thymic and bursal microsomes from chickens p retreated with 3,3',4,4'-tetrachlorobiphenyl (TCB) using a polyclonal antibody against purified P4501A from 3-methylcholanthrene (3-MC)-indu ced chicken embryo liver. A dose-response for induction by TCB of P450 1A protein was detected by Western blotting in both bursal and thymic microsomes. Ethoxyresorufin-O-deethylase (EROD), a specific catalytic activity of P4501A, was also induced in a dose-response fashion. More TCB-induced P4501A was detected in thymus than bursa by both methods. No EROD was detected in bursal or thymic microsomes from untreated chi ckens, although P4501A protein was detected at very low levels in thym ic microsomes from untreated chickens. P4501A was detected by immunohi stochemistry in scattered patches of non-lymphocytic cells residing in medullary regions of the TCB-induced thymus but was not detected in l ymphocytes. This result supports previous work demonstrating that TCB- inducible EROD is much higher in the supporting tissue cell fractions than in lymphocyte fractions of the primary immune tissues. Although E ROD was induced by TCB in the late stage embryo after 20 h exposure, n o effect of TCB on the cell cycle in thymic or bursal lymphocytes was observed over the same period. The same TCB exposure resulted in bursa l but not thymic cellular depletion. Thymic and bursal supporting tiss ue cells may be primary sites of immunosuppression within these organs by P4501A inducers or substrates whether immunosuppression occurs sub sequent to metabolism or through interaction with Ah receptors.