Gender-differences in leukocyte activation in vivo: role of endothelial-derived mediators

1Ramona S. Scotland, 1Johan Duchene, 2Adrian J. Hobbs, 1Amrita Ahluwalia. 1Clinical Pharmacology, William Harvey Research Institute, Queen Mary University of London & 2Wolfson Institute for Biomedical Research, University College London.

A key pro-inflammatory mechanism implicated in cardiovascular disease (CVD) is recruitment of immune cells, which involves interaction of leukocytes with the vascular endothelium. Under basal conditions leukocyte activation is held in check by endothelium-derived mediators, including nitric oxide (NO) and prostacyclin (PGI2). We have recently demonstrated a gender-specific difference in release of these endothelium-derived dilators from the mesenteric vasculature of mice (Scotland et al, 2005). Endothelium-dependent relaxation is mediated predominantly by NO in male arteries but by endothelium-derived hyperpolarizing factor (EDHF) in female arteries. Moreover, in arteries of eNOS-/- or COX-1-/- mice, EDHF does not compensate for the absence of endothelial NO or PGI 2 in males, whereas endothelium-dependent relaxation remains unaltered in female mice irrespective of genotype. In the present study we investigated the impact of gender on basal and cytokine-stimulated leukocyte recruitment in the mouse mesenteric vasculature of eNOS-/- or COX-1-/- mice in vivo.

Intravital microscopy was used to assess leukocyte activation in vivo in male and female wild-type (WT), eNOS-/-, and COX-1-/- mice (11-15g) under basal or acute inflammatory conditions (induced by IL-1β; 5ng i.p.; 90min.). Mice were anaesthetised and the mesenteric vascular bed exteriorised and viewed with a light microscope. Mesenteries were superfused (2ml/min; 37 oC) with bicarbonate-buffered solution (pH 7.4) and post-capillary venules (≥4 vessels/animal, diameter=20-50μm; length≥100µm) chosen at random and leukocyte rolling (cells/min) determined.

Basal leukocyte rolling was low and similar in male and female WT animals (9±1.8, n=11 & 9±3.3, n=4, respectively). In eNOS-/- mice, basal leukocyte rolling was significantly (P<0.05) raised in male (33±5.6, n=8) but not female (7±1.4, n=9) animals. Basal rolling was also significantly (P<0.05) elevated in COX-1-/- mice but no gender-difference was observed (23±4.6, n=4 and 25±3.2, n=8 in males and females, respectively). Exposure to IL-1β, significantly (P<0.05) elevated leukocyte activation in males: 31±9.8 (WT, n=11), 63±9.9 (eNOS-/-, n=6), 86±12.9 (COX-1-/-, n=4) but had no significant effect in females of any genotype: 9±3.2 (WT, n=4), 14±4.5 (eNOS-/-, n=4), 20.9±4.4 (COX-1-/-, n=4).

Thus, endothelial-derived NO is an important modulator of basal and IL-1β-stimulated leukocyte activation in male, but not female, mice. In contrast, basal leukocyte rolling is elevated in both male and female mice in the absence of endothelial PGI2. Since IL-1β is ineffective in stimulating leukocyte rolling in female mice, this indicates that gender-specific, anti-inflammatory mechanisms are present. We have previously demonstrated that EDHF is the predominant endothelium-derived mediator in the mesenteric vascular bed in female mice. Thus, it is likely that enhanced activity of EDHF underlies the gender-differences in leukocyte activation and adds further support to the thesis that EDHF contributes to gender-differences in vascular inflammation and CVD.

Scotland et al (2005). Circulation 111(6):796-803.

This work was supported by The British Heart Foundation