Stress-induced enhancement of leukocyte trafficking into sites of surgery or immune activation

Abstract

Effective immunoprotection requires rapid recruitment of leukocytes into sites of surgery, wounding, infection, or vaccination. In contrast to immunosuppressive chronic stressors, short-term acute stressors have immunoenhancing effects. Here, we quantify leukocyte infiltration within a surgical sponge to elucidate the kinetics, magnitude, subpopulation, and chemoattractant specificity of an acute stress-induced increase in leukocyte trafficking to a site of immune activation. Mice acutely stressed before sponge implantation showed 200-300% higher neutrophil, macrophage, natural killer cell, and T cell infiltration than did nonstressed animals. We also quantified the effects of acute stress on lymphotactin- (LTN; a predominantly lymphocyte-specific chemokine), and TNF-alpha- (a proinflammatory cytokine) stimulated leukocyte infiltration. An additional stress-induced increase in infiltration was observed for neutrophils, in response to TNF-alpha, macrophages, in response to TNF-alpha and LTN, and natural killer cells and T cells in response to LTN. These results show that acute stress initially increases trafficking of all major leukocyte subpopulations to a site of immune activation. Tissue damage-, antigen-, or pathogen-driven chemoattractants subsequently determine which subpopulations are recruited more vigorously. Such stress-induced increases in leukocyte trafficking may enhance immunoprotection during surgery, vaccination, or infection, but may also exacerbate immunopathology during inflammatory (cardiovascular disease or gingivitis) or autoimmune (psoriasis, arthritis, or multiple sclerosis) diseases.

Fig. 1.

Acute stress enhances leukocyte trafficking into an implanted surgical sponge. Saline-treated gelatin sponges were s.c.-implanted in NS or STR mice. Sponges were retrieved at 6, 24, 48, and 72 h after implantation. Compared with NS animals, sponges from STR animals had significantly higher total leukocyte numbers at 6, 24, and 48 h after implantation. STR animals had ≈200% higher macrophage numbers at 6 h, 300% higher neutrophil and macrophage numbers at 24 h, and 200% higher NK cell and T cell numbers at 48 h after implantation. Sponges from NS and STR animals had comparable and lower neutrophil, macrophage, NK cell, and T cell numbers at 72 h, indicating resolution of inflammation in both groups. Data are expressed as means ± SEM. Statistically significant differences between means are indicated (*, P < 0.05; **, P < 0.01, Student's t test).

Fig. 3.

Acute stress further enhances LTN- and TNF-α-directed leukocyte infiltration in a leukocyte subpopulation-specific manner. Neutrophils, macrophages, NK cells, and T cells infiltrating saline-, LTN-, and TNF-α-treated sponges at 6 h after implantation were quantified by using flow cytometry. Compared with sponges from NS animals, sponges from STR animals showed significantly higher macrophage numbers in response to treatment with saline (300% higher), LTN (300% higher), and TNF-α (200% higher). Sponges from STR animals showed higher neutrophil numbers mainly in response to TNF-α. (200%), and higher NK cell (70%) and T cell (100%) numbers only in response to LTN. Therefore, a stress-induced increase in infiltration of macrophages was observed in response to saline, LTN, and TNF-α, but for neutrophils mainly in response to TNF-α, and NK cells and T cells only in response to LTN. Data are expressed as means ± SEM. Statistically significant differences are shown: *, Different from corresponding within-treatment NS group (P <0.05, Tukey's honestly significant difference post hoc test); †, different from NS saline group (P < 0.05, Tukey's honestly significant difference post hoc test).

Fig. 2.

Acute stress increases the magnitude and extent of early leukocyte infiltration into a surgical sponge. Saline-treated gelatin sponges were s.c.-implanted and subsequently retrieved and processed for hematoxylin/eosin staining 6 h after implantation. Compared with NS animals, sponges from STR animals showed dense clusters of leukocytes at the interface between skin tissue and sponge, and a greater extent of infiltration into the adjacent sponge matrix. Arrows point to representative leukocyte clusters. (Scale bar, 100 μm.)