Human neonatal thymectomy induces altered B-cell responses and autoreactivity.

An association between T-cell lymphopenia and autoimmunity has long been proposed, but it remains to be elucidated whether T-cell lymphopenia affects B-cell responses to autoantigens. Human neonatal thymectomy (Tx) results in a decrease in T-cell numbers and we used this model to study the development of autoreactivity. Two cohorts of neonatally thymectomized individuals were examined, a cohort of young (1-5 years post-Tx, n = 10-27) and older children (>10 years, n = 26), and compared to healthy age-matched controls. T-cell and B-cell subsets were assessed and autoantibody profiling performed. Early post-Tx, a decrease in T-cell numbers (2.75 × 109 /L vs. 0.71 × 109 /L) and an increased proportion of memory T cells (19.72 vs. 57.43%) were observed. The presence of autoantibodies was correlated with an increased proportion of memory T cells in thymectomized children. No differences were seen in percentages of different B-cell subsets between the groups. The autoantigen microarray showed a skewed autoantibody response after Tx. In the cohort of older individuals, autoantibodies were present in 62% of the thymectomized children, while they were found in only 33% of the healthy controls. Overall, our data suggest that neonatal Tx skews the autoantibody profile. Preferential expansion and preservation of Treg (regulatory T) cell stability and function, may contribute to preventing autoimmune disease development after Tx.

Cerebral ischemia initiates an immediate innate immune response in neonates during cardiac surgery.

BACKGROUND: A robust inflammatory response occurs in the hours and days following cerebral ischemia. However, little is known about the immediate innate immune response in the first minutes after an ischemic insult in humans. We utilized the use of circulatory arrest during cardiac surgery to assess this. METHODS: Twelve neonates diagnosed with an aortic arch obstruction underwent cardiac surgery with cardiopulmonary bypass and approximately 30 minutes of deep hypothermic circulatory arrest (DHCA, representing cerebral ischemia). Blood samples were drawn from the vena cava superior immediately after DHCA and at various other time points from preoperatively to 24 hours after surgery. The innate immune response was assessed by neutrophil and monocyte count and phenotype using FACS, and concentrations of cytokines IL-1ß, IL-6, IL-8, IL-10, TNFα, sVCAM-1 and MCP-1 were assessed using multiplex immunoassay. Results were compared to a simultaneously drawn sample from the arterial cannula. Twelve other neonates were randomly allocated to undergo the same procedure but with continuous antegrade cerebral perfusion (ACP). RESULTS: Immediately after cerebral ischemia (DHCA), neutrophil and monocyte counts were higher in venous blood than arterial (P = 0.03 and P = 0.02 respectively). The phenotypes of these cells showed an activated state (both P <0.01). Most striking was the increase in the 'non-classical' monocyte subpopulations (CD16(intermediate); arterial 6.6% vs. venous 14%; CD16+ 13% vs. 22%, both P <0.01). Also, higher IL-6 and lower sVCAM-1 concentrations were found in venous blood (both P = 0.03). In contrast, in the ACP group, all inflammatory parameters remained stable. CONCLUSIONS: In neonates, approximately 30 minutes of cerebral ischemia during deep hypothermia elicits an immediate innate immune response, especially of the monocyte compartment. This phenomenon may hold important clues for the understanding of the inflammatory response to stroke and its potentially detrimental consequences. TRIAL REGISTRATION: ClinicalTrial.gov: NCT01032876.

Long-term restoration of the human T-cell compartment after thymectomy during infancy: a role for thymic regeneration?

Thymectomy during early childhood is generally thought to have serious consequences for the establishment of the T-cell compartment. In the present study, we investigated the composition of the T-cell pool in the first 3 decades after thymectomy during infancy due to cardiac surgery. In the first 5 years after thymectomy, naive and total CD4(+) and CD8(+) T-cell numbers in the blood and T-cell receptor excision circle (TREC) levels in CD4(+) T cells were significantly lower than in healthy age-matched controls. In the first years after thymectomy, plasma IL-7 levels were significantly elevated and peripheral T-cell proliferation levels were increased by ∼ 2-fold. From 5 years after thymectomy onward, naive CD4(+) and CD8(+) T-cell counts and TRECs were within the normal range. Because TREC levels are expected to decline continuously in the absence of thymic output, we investigated whether normalization of the naive T-cell pool could be due to regeneration of thymic tissue. In the majority of individuals who had been thymectomized during infancy, thymic tissue could indeed be identified on magnetic resonance imaging scans. Whereas thymectomy has severe effects on the establishment of the naive T-cell compartment during early childhood, our data suggest that functional regrowth of thymic tissue can limit its effects in subsequent years.

FOXP3+ CD4+ Tregs lose suppressive potential but remain anergic during transient inflammation in human.

Tregs are crucial in controlling inflammation. Although the transcription factor FOXP3 is the most applicable phenotype marker of Tregs, it does not indisputably characterize suppressive function during T-cell activation in vitro. A question that remains is: what is the functionality of FOXP3(+) T cells during inflammation in vivo? We studied FOXP3(+) T cells in a human model of acute inflammation due to cardiac surgery. Twenty-five children who underwent cardiac surgery for correction of a septum defect were included. Following surgery, we observed a transient systemic inflammatory response accompanied by an increased proportion of CD25(bright) T cells with sustained Treg phenotype. During this transient immune activation, both the percentage of CD4(+) FOXP3(+) cells and the level of expression of FOXP3 in the CD4(+) CD25(bright) CD127(low) population increased. While Tregs remained present during systemic inflammation and continued to be anergic, the capacity to suppress effector T cells was reduced. The reduced suppressive state of Tregs could be induced in vitro by plasma obtained during the peak of inflammation after surgery. These data show that inflammation inhibits Treg function through soluble factors present in plasma. These results underscore the functional role of FOXP3(+) Tregs during inflammation in vivo.

Hsp70 and cardiac surgery: molecular chaperone and inflammatory regulator with compartmentalized effects.

Open heart surgery is a unique model to study the interplay between cellular injury, regulation of inflammatory responses and tissue repair. Stress-inducible heat shock protein 70-kDa (Hsp70) provides a molecular link between these events. In addition to molecular chaperoning, Hsp70 exerts modulatory effects on endothelial cells and leukocytes involved in inflammatory networks. Hsp70 residing in the intracellular compartment is part of an inhibitory feedback loop that acts on nuclear factor kappaB (NF-kappaB). In contrast, extracellular Hsp70 is recognized by multiple germline-encoded immune receptors, e.g., Toll-like receptor (TLR) 2, TLR4, LOX-1, CD91, CD94, CCR5 and CD40. Hsp70 is thereby able to enhance chemotaxis, phagocytosis and cytolytic activity of innate immune cells and stimulate antigen-specific responses. These apparent contradictory pro- and anti-inflammatory effects of endogenous Hsp70 in the context of cardiac surgery are still not fully understood. An all-embracing model of the compartmentalized effects of endogenous Hsp70 in the orchestration of inflammatory responses in cardiac surgery is proposed.

Bedside prediction rule for infections after pediatric cardiac surgery.

PURPOSE: Infections after pediatric cardiac surgery are a common complication, occurring in up to 30% of cases. The purpose of this study was to develop a bedside prediction rule to estimate the risk of a postoperative infection. METHODS: All consecutive pediatric cardiac surgery procedures between April 2006 and May 2009 were retrospectively analyzed. The primary outcome variable was any postoperative infection, as defined by the Center of Disease Control (2008). All variables known to the clinician at the bedside at 48 h post cardiac surgery were included in the primary analysis, and multivariable logistic regression was used to construct a prediction rule. RESULTS: A total of 412 procedures were included, of which 102 (25%) were followed by an infection. Most infections were surgical site infections (26% of all infections) and bloodstream infections (25%). Three variables proved to be most predictive of an infection: age less than 6 months, postoperative pediatric intensive care unit (PICU) stay longer than 48 h, and open sternum for longer than 48 h. Translation into prediction rule points yielded 1, 4, and 1 point for each variable, respectively. Patients with a score of 0 had 6.6% risk of an infection, whereas those with a maximal score of 6 had a risk of 57%. The area under the receiver operating characteristic curve was 0.78 (95% confidence interval 0.72-0.83). CONCLUSIONS: A simple bedside prediction rule designed for use at 48 h post cardiac surgery can discriminate between children at high and low risk for a subsequent infection.

STAT3 regulates monocyte TNF-alpha production in systemic inflammation caused by cardiac surgery with cardiopulmonary bypass.

BACKGROUND: Cardiopulmonary bypass (CPB) surgery initiates a controlled systemic inflammatory response characterized by a cytokine storm, monocytosis and transient monocyte activation. However, the responsiveness of monocytes to Toll-like receptor (TLR)-mediated activation decreases throughout the postoperative course. The purpose of this study was to identify the major signaling pathway involved in plasma-mediated inhibition of LPS-induced tumor necrosis factor (TNF)-α production by monocytes. METHODOLOGY/PRINCIPAL FINDINGS: Pediatric patients that underwent CPB-assisted surgical correction of simple congenital heart defects were enrolled (n = 38). Peripheral blood mononuclear cells (PBMC) and plasma samples were isolated at consecutive time points. Patient plasma samples were added back to monocytes obtained pre-operatively for ex vivo LPS stimulations and TNF-α and IL-6 production was measured by flow cytometry. LPS-induced p38 mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-κB activation by patient plasma was assessed by Western blotting. A cell-permeable peptide inhibitor was used to block STAT3 signaling. We found that plasma samples obtained 4 h after surgery, regardless of pre-operative dexamethasone treatment, potently inhibited LPS-induced TNF-α but not IL-6 synthesis by monocytes. This was not associated with attenuation of p38 MAPK activation or IκB-α degradation. However, abrogation of the IL-10/STAT3 pathway restored LPS-induced TNF-α production in the presence of suppressive patient plasma. CONCLUSIONS/SIGNIFICANCE: Our findings suggest that STAT3 signaling plays a crucial role in the downregulation of TNF-α synthesis by human monocytes in the course of systemic inflammation in vivo. Thus, STAT3 might be a potential molecular target for pharmacological intervention in clinical syndromes characterized by systemic inflammation.