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In this report, we describe the development of a mini-array system suitable for high-throughput quantification of proteins. This mini-array is a multiplexed, sandwich-type ELISA that measures the concentration of seven different human cytokines--TNF-alpha, IFN alpha, IFN gamma, IL-1 alpha, IL-1 beta, IL-6, and IL-10--from a single sample in each well of a 96-well plate. The mini-array is produced by spotting monoclonal antibodies (mAbs) in a 3 x 3 pattern in the bottom of the wells of 96-well polystyrene plates. Cytokines that are captured by the arrayed mAbs are detected by using biotinylated mAbs, followed by the addition of a streptavidin-horseradish peroxidase (HRP) conjugate and a chemiluminescent substrate. The light produced from the HRP-catalyzed oxidation of the substrate is measured at each spot in the array by imaging the entire plate with a commercially available CCD camera. Here, we demonstrate that these 96-well-plate format mini-arrays have performance characteristics that make them suitable for the high-throughput screening of anti-inflammatory compounds.

We investigated the pattern of down-regulation of cytokine production in endotoxin (lipopolysaccharide [LPS]) tolerance. A 4-day treatment with LPS (35 micrograms per mouse) was followed by a challenge on day 6 with one more injection of LPS. Circulating tumor necrosis factor (TNF) and interleukin-6 (IL-6) could not be induced (> 99% inhibition) by LPS in LPS-tolerant mice; colony-stimulating factor (CSF) was also down-regulated by more than 95%, whereas interferon (IFN) and IL-1 syntheses were only partially inhibited. To study the mechanism of cytokine down-regulation in tolerance, we attempted to reverse the tolerant state by pretreatment with phorbol 12-myristate 13-acetate (PMA) (4 micrograms per mouse) 10 min before the LPS challenge. PMA completely restored IL-6 production and partially that of CSF. PMA had no effect on IFN production and inhibited the induction of IL-1. TNF production was also not restored by PMA. To investigate the role of endogenously produced cytokines in the development of LPS tolerance, we administered IL-6, TNF, or IL-1 alpha, using the same treatment schedule as that for LPS. Whereas IL-6 had no effect, IL-1 alpha or TNF induced partial tolerance to LPS in terms of inhibition of LPS-stimulated TNF and IL-6 production. However, a full LPS-tolerant state could not be induced by administration of recombinant cytokines, suggesting the existence of additional mechanisms, such as a loss of LPS receptors or changes in release of soluble binding proteins.

When administered parenterally, endotoxin stimulates the synthesis of IL-1, TNF-alpha, and IL-6. However, this initial injection induces tolerance; a second injection of endotoxin results in lower levels of circulating cytokines. In our study, five healthy male volunteers between the ages of 18 and 30 were injected with Escherichia coli endotoxin. Four subjects received only saline. Immediately before the injection and 3, 6, and 24 h afterward, PBMC were isolated and stimulated in vitro with endotoxin, IL-1, or toxic shock syndrome toxin-1. Inasmuch as CD14+ monocytes are the primary source of the cytokines induced by these stimuli, results are expressed as cytokine production per 10(6) CD14+ cells. Six h after endotoxin injection, endotoxin-stimulated CD14+ cells synthesized 66% less IL-1 beta (p < 0.01), 47% less TNF-alpha (p < 0.001), 56% less IL-6 (p < 0.01), and 49% less IL-8 (p < 0.01) than cells obtained before the injection. This suppression was not specific for endotoxin; IL-1 beta-induced IL-1 alpha and TNF-alpha were reduced by 84% (p = 0.01) and 68% (p < 0.001), respectively. A decrease in cytokine synthesis was also observed using toxic shock syndrome toxin-1 as a stimulus: 57% for IL-1 beta (p = 0.06), 70% for TNF-alpha (p < 0.01), 56% for IL-6 (p < 0.05), and 71% for IL-8 (p = 0.001). When data were expressed as cytokine production per 10(6) PBMC, cells isolated 3 h after endotoxin injection synthesized significantly less stimulus-induced IL-1, TNF-alpha, IL-6, and IL-8 than did PBMC from saline-injected controls. We conclude that endotoxin tolerance is due, in part, to changes in the stimulus-induced cytokine response of circulating CD14+ cells.

Cytokines such as interleukin 1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), and interleukin 6 (IL-6) mediate a variety of host responses to trauma and infection, including skeletal muscle proteolysis. This investigation assesses the influence of damaging eccentric exercise on in vitro production and plasma concentrations of cytokines and their relationship to muscle protein breakdown. In a double-blind placebo-controlled protocol, 21 male subjects took vitamin E supplements (800 IU/day) for 48 days, then ran downhill on an inclined treadmill. Twenty-four hours after this single session of eccentric exercise, endotoxin-induced secretion of IL-1 beta was augmented 154% (P less than 0.01) in cells obtained from the placebo subjects, but no significant exercise-related changes were observed in cells from the vitamin E-supplemented subjects. TNF-alpha secretion was also significantly increased 24 h after exercise, but the response was not inhibited by vitamin E. In contrast, IL-6 secretion did not change after exercise, but dietary vitamin E supplementation significantly reduced IL-6 secretion throughout the 12-day period of observation (P = 0.023). Urinary 3-methylhistidine excretion correlated with mononuclear cell secretion of both IL-1 beta (P less than 0.05) and prostaglandin E2 (P less than 0.05), supporting the concept that these mononuclear cell products contribute to the regulation of muscle proteolysis.