Alcohol (EtOH) is a well-documented immunosuppressant. Acute EtOH-induced immunosuppression is partially due to suppression of tumor necrosis factor ␣ (TNF-␣) secretion. We investigated the mechanism of acute EtOH-induced TNF-␣ suppression in two monocytic cell lines, Mono Mac 6 and DRM. EtOH inhibited TNF-␣ secretion in a dosedependent manner. However, TNF-␣ transcription was not affected by EtOH. Enzyme-linked immunosorbent assay and confocal microscopy showed that EtOH treatment increased cell-associated TNF-␣. Ectodomain shedding of TNF-␣ from the cell surface is mediated by TNF-␣ converting enzyme (TACE). In contrast with TNF-␣, EtOH did not inhibit interleukin-8 (IL-8) secretion, which does not require shedding. Furthermore, TNF p75 receptor shedding, a biomarker for TACE activity, was inhibited by EtOH in both cell lines. EtOH also inhibited TNF p75 receptor shedding in TACE-reconstituted fibroblasts, suggesting that EtOH inhibits the shedding process. These data show that acute EtOH exposure can posttranscriptionally suppress TNF-␣ production, resulting in specific defects in immune defense.