Immune response accelerated telomere shortening during early life stage of a passerine bird, the blue tit (Cyanistes caeruleus)

Abstract

Dealing with infections is a daily challenge for wild animals. Empirical data show an increase in reactive oxygen species (ROS) production during immune response. This could have consequences on telomere length, the end parts of linear chromosomes, commonly used as proxy for good health and ageing. Telomere length dynamics may reflect the costs associated with physiological responses. In this study, immune system of blue tit (Cyanistes caeruleus) nestlings was experimentally challenged through a polyinosinic:polycytidylic acid (poly I:C) injection, a synthetic double-stranded RNA that mimics a virus, activating the pathway of immune response triggered via the toll-like receptors 3. This path is known to form ROS downstream. Immune response was quantified by white cell counts in blood, while brain lipoperoxidation has been evaluated as an indicator of oxidative damage. Finally, individuals' telomere length shortening between days 8 and 15 after hatching was measured in erythrocytes. Challenged nestlings showed increased leukocyte number when compared with control (treated with a saline solution), lower brain lipid peroxidation (likely as a result of a compensatory mechanism after oxidative stress burst) and accelerated telomere shortening. These findings support the 'ageing cost of infections pathway' hypothesis, which supposes a role for infections in quick biological ageing.

Keywords: blue tit; immune system; poly I:C; reactive oxygen species; telomere; virus.

Figure 1.

Boxplots of scaled number of leukocytes compared with erythrocytes at day 15 for control and treatment.

Figure 2.

Overall regression between brain lipoperoxidation at day 15 and immune response estimated as the number of leukocytes compared with erythrocytes in blood smears at day 15.

Figure 3.

Boxplots of scaled telomere length variations in per cent between days 8 and 15. Values greater than 0 correspond to telomere lengthening, negative values to shortening.