Infection withMycoplasma gallisepticumBuffers the Effects of Acute Stress on Innate Immunity in House Finches

Abstract

When wild animals become infected, they still must cope with the rigors of daily life, and, thus, they still can be exposed to acute stressors. The suite of physiological responses to acute stress includes modifying the innate immune system, but infections can also cause similar changes. We examined the effects of an acute stressor (capture stress) on leukocyte abundance and bacteria-killing ability (BKA) in wild birds (house finches Haemorhous mexicanus) with and without a naturally occurring infection (Mycoplasma gallisepticum) to determine whether infection alters the typical immune response to stress. Birds were captured and bled within 3 min (baseline sample) and then held in paper bags for 2 h and bled again (stress sample). From blood smears made at both time points, we obtained estimates of total white blood cell (WBC) counts and relative numbers of each cell. We also measured BKA of plasma at both time points. In uninfected birds (n = 26), total WBC count decreased by 30% over time, while in infected birds (n = 9), it decreased by 6%. Relative numbers of heterophils did not change over time in uninfected birds but increased in infected birds. Combined with a reduction in lymphocyte numbers, this led to a threefold increase in heterophil-lymphocyte values in infected birds after the stressor, compared to a twofold increase in uninfected birds. There was a nonsignificant tendency for BKA to decline with stress in uninfected birds but not in diseased birds. Collectively, these results suggest that infections can buffer the negative effects of acute stress on innate immunity.

Common measures of immune function vary with time of day and sampling protocol in five passerine species

“…30 min, 60 min or even 2.5 h after capture). Several of these studies reported a discernible difference in immune function between individuals sampled within 3 min of capture versus those sampled 30 min or more after capture, especially in the case of bactericidal activity (Buehler et al, 2008;Davis, 2005;Fratto et al, 2014;Matson et al, 2006;Millet et al, 2007). It remains unknown whether measures of innate immune function in wild birds vary with capture stress over shorter time intervals; however, it is variation over these shorter time intervals that is likely to be the most relevant for field studies using mist nets or walk-in traps, given that welfare considerations dictate individuals be processed expeditiously post-capture, with the result that blood samples are more likely to be collected within minutes rather than hours of capture.…”

Differing House Finch Cytokine Expression Responses to Original and Evolved Isolates of Mycoplasma gallisepticum

“…The house finch–MG interaction has become an important natural model of coevolution between a host and an emerging pathogen, facilitating insights into fundamental issues in disease ecology and evolutionary biology ( 18 , 20 , 21 ). However, we still have only a limited understanding of the key immunological features of the house finch response to MG. Several studies show that house finch immune responses to MG are associated with hematological changes ( 22 , 23 ) and antigen-specific antibody production in both lachrymal fluid and blood ( 9 , 24 ). Nevertheless, the protective effects of humoral immunity remain unclear ( 19 ).…”