Additional file 8 of Proof of concept for multiplex detection of antibodies against Chlamydia species in chicken serum using a bead-based suspension array with peptides as antigens

Additional file 8. Seroreactivity of C. psittaci and C. abortus derived peptides with sera from immunized chickens. In addition to observations on seroreactivity of peptides derived from C. gallinacea and C. psittaci, immunizations were performed with bacterins of home-grown C. psittaci and various commercial Chlamydia preparations (Virion/Serion); material of C. avium was not available. At the start of the experiment all chickens showed no signals exceeding the cutoffs, except chicken 145 (n = 1) and 172 (n = 2), where the signals by serum from chicken 172 were relatively high (> 1000). In the final bleeds of chickens immunized with C. psittaci bacterins, antibodies were present against a subset of C. psittaci peptides. Two out of four of these chickens also showed reactivity to one C. abortus peptide, one chicken showed a very low cross-reactivity toward a C. gallinacea peptide. The immunization with C. abortus bacterin in one chicken resulted in high signals on two C. abortus peptides. This suggests that chickens are capable of an immune response to at least a subset of the C. abortus peptides. Both C. abortus-immunized chickens showed also high signals on two C. avium peptides in the final bleeds: this cross-reactivity was not observed in infected mice (Figure 1, Additional file 1) and also not in field samples (no coincidence of signals against C. abortus and C. avium peptides, Figure 4). Chickens immunized with bacterins of two other species (C. pneumoniae and C. trachomatis) only in one case gave a modest signal with one C. psittaci peptide. In addition, chicken sera from the same experiment as the C. psittaci sera used for Figure 2, that were immunized after an ineffective infection, resulted in a specific immune response to most C. psittaci peptides. The panel recognized is broader than what is seen upon an infection experiment (Figure 2, Additional file 2). Taken together these results provide some additional evidence for seroreactivity of a subset of peptides in chicken sera. Observed cross-reactivities may suggest that the immune response upon immunization is different from that upon an infection: signals are high, more peptides are recognized, and even some very significant cross-reactivity is observed (with C. avium peptides).