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

FERNANDEZ G.C; RAMOS M.V; BENTANCOR LV; FERNANDEZ-BRANDO R.J; LANDONI V.I; EXENI R; GRIMOLDI I; LASO MC; EXENI A,; ELIAS-COSTA C,; VALLEJO G; ISTURIZ M.A; PALERMO M.S

Buenos Aires Argentina

Congreso; 7th International Symposium on Shiga Toxin (Verocytotoxin)-producing Escherichia coli Infections; 2009

Asociación Argentina de Microbiología

Lower response of monocytes towards Lipopolysaccharide in severe cases of Hemolytic Uremic Syndrome Fernández GC., Ramos MV., Bentancor LV, Fernández-Brando RJ, Landoni VI., Exeni R, Grimoldi I, Laso MC, Exeni A, Elias-Costa C, Vallejo G, Isturiz MA, Palermo MS. 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, 37ºC) 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±138,LPS=2033±243*; mHUS: basal=1970±766,LPS=3182±1080§#; sHUS: 1881±232,LPS=2306±643; IC: basal=2044±210*,LPS=2358±252; 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±50,LPS=429±160*; mHUS: Basal=185±30,LPS=493±104§; sHUS: Basal=121±43,LPS=216±48Ф♦; IC: Basal=183±33,LPS=355±60‡; p<0.05 vs: *basal HC, §basal mHUS,  Фbasal sHUS, ‡basal 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±0.8,LPS=6.1±0.9; mHUS: basal=12.8±1.4*,LPS=5.6±0.5§; sHUS: basal=17.7±1.1*,LPS=11.8±1.7#¶; IC: basal=16.0±12.2*,LPS=8.6±1.7‡; p<0.05 vs: *basal HC, #LPS HC, §basal mHUS, ¶LPS mHUS, ‡basal 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.