INCREASED EXPRESSION OF TOLL-LIKE RECEPTOR-2 AND -4 ON LEUKOCYTES FROM PATIENTS WITH SEPSIS

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Abstract
The reduced responsiveness of monocytes or granulocytes toward endotoxin (endotoxin tolerance) during sepsis may depend on Toll-like receptors (TLR). The expression of TLR-2 and TLR-4 was measured on neutrophils (PMN) and monocytes from patients with sepsis (n = 21) or healthy controls (n = 12). Leukocytes (1 × 106/mL) were incubated at 37°C with or without a TLR-4 (LPS 1 μg/mL) or a TLR-2 ligand (MALP-2 2 nM). Surface expression of TLR-2 and TLR-4 at 0, 4, and 16 h was determined in FACS after staining with specific antibodies. The release of IL-8 and TNF-α was measured by ELISA. Freshly isolated PMN from patients with sepsis exhibited significantly (P < 0.05) higher mean fluorescence for TLR-2 (78.0 ± 18.6) and TLR-4 (11.4 ± 2.3) than controls (12.8 ± 2.2 and 2.3 ± 0.4). Similarly, monocytes from patients exhibited higher TLR-2 and TLR-4 expression (300.8 ± 40.6 and 92.7 ± 12.1) than cells from controls (149.5 ± 27.1 and 52.2 ± 7.6). In patients with sepsis, expression of TLR-2 and TLR-4 on PMN increased during 16 h of incubation (106.2 ± 22.1 and 34.5 ± 5.3), whereas it remained unchanged in controls (19.3 ± 6.1 and 5.4 ± 1.9). Incubation with LPS or MALP-2 had no effect on TLR-4 or TLR-2 expression in cells from either controls or patients. Despite increased TLR expression in cells from patients with sepsis, the endotoxin-induced release of TNF-α and IL-8 was indistinguishable from that in controls. Therefore, the endotoxin tolerance seen in patients with sepsis does not depend solely on TLR-2 or TLR-4 expression, and other mechanisms must be involved.