PCR DIFFERENTIAL DISPLAY OF IMMUNE GENE-EXPRESSION IN TRICHOPLUSIA NI

The immune state of insects is defined by a set of proteins that is ab sent in the naive state, To explore the immune system of Trichoplusia ni in more detail we have employed a PCR differential display techniqu e to compare the mRNA population of untreated last instar larvae to th at of immunized animals, In the primary display, more than one hundred bands seemed induced upon bacterial challenge, When they were used as probes in Northern blots, 35% of these probes detected inducible mRNA species, Such probes were used to screen a cDNA library from immunize d larvae. We isolated clones for T, ni homologs of cecropin A, lysozym e and attacin. One differentially expressed band hybridized to clones for BJHSP1, a hemacyanin-related protein which is hormonally up-regula ted in last instar larvae; this induction is probably not related to t he bacterial infection, Still other probes recognized inducible mRNAs of 1.6 and 1.0 kb, The corresponding cDNA clones did not show strong s equence homology to any known proteins, We have demonstrated the poten tial of this PCR technique to display both known and unknown genes spe cific for the immune state of whole insects against a background of ge nes involved in larval development.