IMMUNOTOLERANCE AGAINST A FOREIGN ANTIGEN TRANSGENICALLY EXPRESSED INTHE LENS

PURPOSE. TO extend our knowledge concerning immunotolerance against au tologous lens crystallins, transgenic (Tg) mice that express a foreign antigen in their lens were generated, and the immune response against the antigen in these mice was analyzed. METHODS. Conventional techniq ues were used to generate lines of Tg mice that express soluble (S-) o r membrane-bound (M-) hen egg lysozyme (HEL) under the control of the alpha A-crystallin promoter. The presence of HEL in various organs was determined by the particle concentration fluorescence immunoassay (PC FIA), and reverse transcription-polymerase chain reaction technique wa s used to detect mRNA transcripts of the molecule. To examine the deve lopment of immunity (or tolerance), Tg mice and their wild-type contro ls were immunized with HEL (25 mu g) in Freund's complete adjuvant and 14 days later were tested for immune response against the antigen. Ce llular immunity was measured by the lymphocyte proliferation assay and cytokine production, and humoral immunity was determined by enzyme-li nked immunosorbent assay. RESULTS. Eyes of the high copy number M-HEL Tg mice were dystrophic, with disrupted lens, whereas no morphologic c hanges were detected in the eyes of the other Tg mouse lines, All Tg m ice exhibited tolerance to HEL by their cellular and humoral immune co mpartments. The state of immunotolerance to HEL was retained in the Tg mice for as long as 10 months after removal of the main depot of this protein, by enucleation. Measurable amounts of HEL were found in the eyes of all Tg mice, but the protein could not be detected in the seru m or in other organs by the sensitive PCFIA (with a threshold of 1 ng/ ml). Yet, HEL mRNA was found in the thymus of the Tg mice, suggesting that minute amounts of the protein are expressed in this organ. CONCLU SIONS. The unresponsiveness to HEL in the Tg mice seems to be due to a ''central'' mechanism of tolerance, mediated by a minuscule amount of HEL in the thymus. Conversely, the much larger amounts of HEL in the peripheral depot, the eyes, play a minor role if any in the tolerogeni c process. It is further proposed that a similar mechanism of central tolerance is responsible for the immunotolerance against autologous le ns crystallins.