Upregulation of CD44 expression on bovine articular chondrocytes induced by synthetic lipid A

Abstract The purpose of the study reported in this article was to investigate effects of synthetic lipid A on the expression of adhesion molecule CD44 on bovine articular chondrocytes. Full-thickness bovine articular cartilage was dissected from the carpometacarpal joints of 24 cows. Cartilage pieces were enzymatically digested to liberate chondrocytes. The chondrocytes were incubated in the presence of synthetic lipid A in suspension culture. Cell characteristics and binding of monoclonal antihuman CD44 antibodies were assessed with a flow cytometer. The expression of CD44 mRNA in chondrocytes was detected by reverse transcription-polymerase chain reaction (RT-PCR) technique. PCR products were quantified with a charge-coupled device image sensor. The percentage of CD44-positive chondrocytes was 42.2% ± 12.0%, 51.7% ± 6.8%, and 51.1% ± 5.0%, in the presence of lipid A at 0.25 μg/ml, 2.5 μg/ml, and 25 μg/ml, respectively, whereas it was 39.2% ± 8.9% in the absence of lipid A. In flow cytometry, two subpopulations of chondrocytes were found in each of five separate experiments, one with smaller number of forward scatter (FS) and the other with larger number of FS. The percentage of CD44-positive cells was 24.8% ± 8.5% in the subpopulation with smaller number of FS and 31.9% ± 6.4% in the subpopulation with larger number of FS at time 24 h after incubation. The bacterial component, lipid A, upregulated expression of CD44 on articular chondrocytes.