Inter- and intraindividual variation of endotoxin- and beta(1 --> 3)-glucan-induced cytokine responses in a whole blood assay

Abstract

Inflammatory airway responses to bioaerosols and to their active compounds, such as endotoxin and beta(1 --> 3)-glucan, vary between individuals. These differences may be explained by variation in cytokine responsiveness, which can be assessed by in vitro stimulation tests with isolated blood leukocytes or lung macrophages. In large-scale population studies, ex vivo induced cytokine production may also be tested with a more simple 'whole blood assay' (WBA). However, applicability of a WBA to characterize a subject's responsiveness depends largely on its reproducibility. This study was conducted to: 1) assess the within- and between-subject variability in cytokine production in a WBA after stimulation with endotoxin or beta(1 --> 3)-glucan; and 2) to determine under which conditions this test is most discriminating between subjects and most reproducible within subjects. Blood was collected from 14 healthy volunteers, of whom 10 also participated on a second occasion. Each blood sample was used in two WBA tests; the first WBA was initiated two hours and the second 26 hours after venapuncture. The WBA test itself comprised overnight incubation with serial dilutions of endotoxin [lipopolysaccharide (LPS)] and curdlan (a beta(1 --> 3)-glucan), after which blood cell supernatant was collected. Interleukin(IL)-1beta, IL6, IL8 and tumor necrosis factor alpha (TNFalpha) were determined in the supernatant. In all individuals, a dose-dependent production of cytokines was observed for both LPS and curdlan. For all cytokines, variation between subjects was higher than within subjects, and this was most pronounced for IL1beta and IL6. There was moderate-to-high correlation in the induced release of all four cytokines, and between cytokine release induced by LPS or curdlan. Optimal stimulation concentrations were 6.25 and 12.5 ng/mL for endotoxin and 12500 and 25000 ng/mL for curdlan. Cytokine production in WBA initiated 26 hours after venapuncture showed lower between-subject and larger within-subject variance, thus favoring an early initiation of the assay. In conclusion, measuring endotoxin- or glucan-induced cytokine production in a WBA initiated within two hours after venapuncture appears to be an effective method to determine a person's cytokine responsiveness, at least in healthy naive subjects.