Evaluation of the effects of dexamethasone-induced stress on levels of natural antibodies in immunized laying hens

Natural antibodies (NAb) are an important humoral component of innate immunity, playing a pivotal role as first line of defence against pathogens even without prior antigen-specific activation or antigen-driven selection. The levels of NAb in plasma of young laying hens were explored in more detail and identified 2,4,6-trinitrophenyl bovine serum albumin (TNP-BSA), as the non-self antigen showing the highest levels of IgΥ- and IgM-NAb. Subsequently, the relation between specific antibody (SpAb) levels and NAb levels, and the effect of dexamethasone (DEX)-induced stress on the acquired Ab response and on NAb levels were examined. According to obtained results, the affinity of NAb and SpAb, measured using the thiocyanate elution method, resulted higher in SpAb than in NAb. After stress induction, IgM-NAb and SpAb levels showed a transient decrease, whereas the levels of IgΥ-NAb were not changed. Moreover, statistical analysis showed positive correlations between IgΥ- and IgM-NAb levels and between IgM-NAb and SpAb levels that are lost as stress has been induced, whereas no correlation was observed between IgΥ-NAb and SpAb levels, neither before nor after the DEX-administration. This indicates that IgM-NAb assessment could be a valid tool to estimate the potential of the acquired Ab response and that the dexamethasone-induced stress condition causes depression of IgM-NAb levels and the acquired Ab response, but it has no evaluable effects on IgΥ-NAb levels.