Ramón Exeni

Impaired neutrophils in children with the typical form of hemolytic uremic syndrome

Experimental and clinical evidence suggest that activated neutrophils (PMN) could contribute to endothelial damage in Hemolytic Uremic Syndrome (D+HUS). Additionally, while PMN-activating cytokines and PMN-derived products have been found in D+HUS sera, we have demonstrated phenotypic alterations in D+HUS PMN compatible with a deactivation state. Here, we investigated whether D+HUS PMN were actually hyporesponsive, and explored some of the mechanisms probably involved in their derangement. Twenty-two D+HUS children were bled in the acute period, and blood samples from healthy, acute uremic and neutrophilic children were obtained as controls. We evaluated degranulation markers in response to cytokines, intracellular granule content, and reactive oxygen species (ROS) generation in circulating D+HUS and control PMN. The influence of D+HUS-derived plasma and the direct effects of Stx in vitro were evaluated on healthy donors’ PMN. We found that D+HUS PMN presented reduced degranulatory capacity in response to cytokines and intracellular granule content, and decreased ROS generation. D+HUS plasma or Stx did not affect the phenotype and function of healthy donors’ PMN. These results suggest that upon hospitalization D+HUS PMN are functionally impaired and show features of previous degranulation, indicating a preceding process of activation with release of ROS and proteases involved in endothelial damage.

Differential expression of function-related antigens on blood monocytes in children with hemolytic uremic syndrome

Monocytes (Mo) mediate central functions in inflammation and immunity. Different subpopulations of Mo with distinct phenotype and functional properties have been described. Here, we investigate the phenotype and function of peripheral Mo from children with hemolytic uremic syndrome (HUS). For this purpose, blood samples from patients in the acute period of HUS (HUS AP) were obtained on admission before dialysis and/or transfusion. The Mo phenotypic characterization was performed on whole blood by flow cytometry, and markers associated to biological functions were selected: CD14 accounting for lipopolysaccharide (LPS) responsiveness, CD11b for adhesion, Fc receptor for immunoglobulin G type I (FcγRI)/CD64 for phagocytosis and cytotoxicity, and human leukocyte antigen (HLA)‐DR for antigen presentation. Some of these functions were also determined. Moreover, the percentage of CD14+ CD16+ Mo was evaluated. We found that the entire HUS AP Mo population exhibited reduced CD14, CD64, and CD11b expression and decreased LPS‐induced tumor necrosis factor production and Fcγ‐dependent cytotoxicity. HUS AP showed an increased percentage of CD14+ CD16+ Mo with higher CD16 and lower CD14 levels compared with the same subset from healthy children. Moreover, the CD14++ CD16– Mo subpopulation of HUS AP had a decreased HLA‐DR expression, which correlated with severity. In conclusion, the Mo population from HUS AP patients presents phenotypic and functional alterations. The contribution to the pathogenesis and the possible scenarios that led to these changes are discussed.

Role of Polymorphonuclear Leukocytes in the Pathophysiology of Typical Hemolytic Uremic Syndrome

Thrombotic microangiopathy and acute renal failure are cardinal features of post-diarrheal hemolytic uremic syndrome (HUS). These conditions are related to endothelial and epithelial cell damage induced by Shiga toxin (Stx), through an interaction with its globotriaosylceramide (Gb3) receptor. Although, Stx is the main pathogenic factor and necessary for HUS development, clinical and experimental evidence suggest that the inflammatory response is able to potentiate Stx toxicity. Lipopolysaccharides (LPS) and neutrophils (PMN) represent two central components of inflammation during a Gram-negative infection. In this regard, patients with high peripheral PMN counts at presentation have a poor prognosis. In the present review, we discuss the contribution of experimental models and patients studies in an attempt to elucidate the pathogenic mechanisms of HUS.

Low levels of serum erythropoietin in children with endemic hemolytic uremic syndrome

Abstract. Serum erythropoietin (EPO) levels were measured in ten previously non-transfused children with hemolytic uremic syndrome (HUS). Complete blood cell count, serum EPO, and renal function tests were carried out upon admission and weekly thereafter. Blood samples were obtained: (1) prior to the first transfusion; (2) after the first transfusion but before recovery from renal failure; (3) during the recovery stage. All patients required transfusions (mean 1.8±0.8 per child). Absolute values of EPO correlated positively with the hematocrit during the three stages (r = 0.53, 0.36, and 0.12, respectively) which is opposite to expected results. The observed EPO logarithm/predicted EPO logarithm upon admission was low (0.70±0.08), falling further during stage 2 (0.57±0.03), but increasing thereafter (0.78±0.07) without reaching normal values. The reticulocyte production rate followed a parallel course (0.74±0.14, 0.54±0.11, and 0.60±0.10, respectively). On comparing the observed serum EPO levels with those expected, 9 of 11 pre-transfusion samples showed low values; in stage 2, all samples were below normal; in the recovery phase most (77.8%) were still low. Our results show an inadequate EPO synthesis in children with HUS, which could play an important pathogenic role, since it aggravates the severity of the existing hemolytic anemia; the secondary inhibitory effect of repeated transfusions exacerbates this inadequate synthesis.