Lower response of monocytes towards Lipopolysaccharide in severe cases of Hemolytic Uremic Syndrome

FERNÁNDEZ G.C; RAMOS M.V; BENTANCOR, L.V; FERNANDEZ-BRANDO R.J; LANDONI V.I; EXENI R.; GRIMOLDI I.; LASO M.C.; EXENI A.; ELIASCOSTA C.; VALLEJO G.; ISTURIZ M.A.; PALERMO M.S

Buenos Aires

Simposio; 7th International Symposium on Shiga Toxin (Verocytotoxin) Producing E.coli Infections.; 2009

Asociación Argentina de Microbiología

Lipopolysaccharide (LPS) is the main component of the cell wall of Shiga toxin producing Gram-negative organisms. The repetitive exposure to LPS induces a refractory state towards its effects, known as tolerance to LPS. Monocytes (Mo) are particularly susceptible to LPS effects. We have previously demonstrated phenotypical alterations in function-related membrane antigens in Mo of HUS patients. Here, we evaluated whether Mo of HUS patients are low responders to LPS as a consequence of a previous exposure to this inflammatory mediator. For this purpose, we determined the variation of different membrane markers of Mo after LPS incubation (1 mg/ml, 4h, 37¨¬C) by flow cytometry. Patients were divided in two groups, mild cases (mHUS, no anuria, no dialysis, n=11) and severe cases (sHUS, presence of anuria and need of dialysis, n=10). Healthy children (HC, n=20) and children with infections not related to HUS (IC, n=10) were included as controls. After LPS incubation the mean fluorescence intensity (MFI) of CD14 increased only in HC and mHUS (MFI CD14: HC: basal=1373¡¾138,LPS=2033¡¾243*; mHUS: basal=1970¡¾766,LPS=3182¡¾1080¡×#; sHUS: 1881¡¾232,LPS=2306¡¾643; IC: basal=2044¡¾210*,LPS=2358¡¾252; p<0.05 vs: *basal HC, #LPS HC, ¡×basal mHUS). LPS increased HLA-DR expression in all groups, although the level reached in sHUS was statistically lower (MFI HLA-DR: HC:  basal=211¡¾50,LPS=429¡¾160*; mHUS: Basal=185¡¾30,LPS=493¡¾104¡×; sHUS: Basal=121¡¾43,LPS=216¡¾48¬¶♦; IC: Basal=183¡¾33,LPS=355¡¾60¢Ô; p<0.05 vs: *basal HC, ¡×basal mHUS,  ¬¶basal sHUS, ¢Ôbasal IC, ♦LPS of all other groups). mHUS, sHUS and IC groups showed an increased percentage (%) of the CD16+ subset compared to HC. This % decreased after LPS incubation in mHUS and IC, reaching similar values than those observed in HC, but remained high in sHUS (% CD16+ Mo: HC: basal=7.9¡¾0.8,LPS=6.1¡¾0.9; mHUS: basal=12.8¡¾1.4*,LPS=5.6¡¾0.5¡×; sHUS: basal=17.7¡¾1.1*,LPS=11.8¡¾1.7#¢Ò; IC: basal=16.0¡¾12.2*,LPS=8.6¡¾1.7¢Ô; p<0.05 vs: *basal HC, #LPS HC, ¡×basal mHUS, ¢ÒLPS mHUS, ¢Ôbasal IC). Whereas the response to LPS is attenuated in sHUS Mo, mHUS Mo behave similar to HC. A higher exposure to LPS in sHUS could explain the lower response observed in this group.