Receptor-interacting protein-2 deficiency delays macrophage migration and increases intracellular infection during peritoneal dialysis-associated peritonitis

BACKGROUND

Early upregulation of receptor-interacting protein-2 (RIP2) expression during peritoneal dialysis (PD)-associated peritonitis correlates with a favorable clinical outcome, while failure to upregulate RIP2 correlates with a protracted course. We noticed that patients who do not upregulate RIP2 during PD-associated peritonitis have more peritoneal macrophages during the early phase of infection.

METHODS

To study the mechanism behind this observation, we examined the role of RIP2 in the immune response to bacterial challenge in a mouse model of acute peritonitis. We injected RIP2(+/+) and RIP2(-/-) mice intraperitoneally with a Staphylococcus epidermidis cell free-preparation, and peritoneal cells were isolated 3, 6 and 24 h after challenge.

RESULTS

Surprisingly, RIP2(-/-) mice had a comparable influx of inflammatory leukocytes, but had a significantly higher number of peritoneal macrophages at 3 h, indicating delayed emigration of these cells. No significant differences were seen at later times suggesting that migration was delayed but not inhibited. In addition, RIP2(-/-) macrophages were more permissive to intracellular infection by Staphylococcus aureus, indicating that, in the absence of RIP2, resident peritoneal macrophages could become reservoirs of bacteria.

CONCLUSION

These findings provide a mechanism for the observation that upregulation of RIP2 expression is required for rapid resolution of peritonitis, by decreasing intracellular infection and by regulating the migration of antigen-presenting cells in the early stages of an inflammatory response.

Receptor-interacting protein 2 is a marker for resolution of peritoneal dialysis-associated peritonitis

There are no predictive factors for peritoneal dialysis-associated peritonitis; however, its resolution correlates with a cell-mediated Th1 immune response. We tested the hypothesis that induction of receptor-interacting protein 2 (RIP2), an assumed kinase linked with Th1 responses, is a useful marker in this clinical setting. Basal RIP2 expression was measured in human immune cells and during dialysis-associated peritonitis. RIP2 increased with bacterial toxin cell activation and the temporal profile for this differed depending on immune cell involvement in the innate or adaptive phases of the response. Importantly, RIP2 expression increased in peritoneal immune cells during dialysis-associated peritonitis and this upregulation correlated with clinical outcome. An early induction in peritoneal CD14(+) cells correlated with rapid resolution, whereas minimal induction correlated with protracted infection and with catheter loss in 36% of patients. These latter patients had higher levels of MCP-1 consistent with a delayed transition from innate to adaptive immunity. Our study shows that upregulation of RIP2 is a useful marker to monitor dialysis-associated peritonitis and in predicting the clinical outcome of these infections.

Blood pressure, volume, and sodium control in an automated peritoneal dialysis population

OBJECTIVES

To examine the control of blood pressure and volume, and the role of sodium removal in a single, large, contemporary, automated peritoneal dialysis (APD) population where icodextrin is used liberally and there is a policy to avoid long duration glucose-based daytime dwells.

DESIGN

Observational cross-sectional study.

SETTING

A university hospital.

PATIENTS

56 APD patients, with a mean duration on peritoneal dialysis of 1.9 years; 50% were prescribed icodextrin.

MAIN OUTCOME MEASURES

Blood pressure, extracellular water volume (ECW)-to-intracellular water volume (ICW) ratio, and total (peritoneal and urinary) sodium removal.

RESULTS

Sodium Removal: Mean total sodium removal, while low at 102.9 +/- 64.6 mmol/day, showed a wide range, with 41% having a sodium removal of >120 mmol/day. Total sodium removal correlated with total body water, ECW, and ICW (p < 0.001, p < 0.001, p < 0.025, respectively), as well as with height and weight (p < 0.06, p < 0.01 respectively). On multivariate analysis, only ultrafiltration volume and urine volume were significantly associated with total sodium removal (r(2) = 0.67, p < 0.0001 for both). There was also a correlation between sodium removal and urea nitrogen appearance (r(2) = 0.31, p < 0.001), with urea nitrogen appearance in turn being closely correlated with ICW (p < 0.001). Volume Status: The ECW/ICW ratio was 0.88 +/- 0.17, which was not significantly different to that found in hemodialysis patients without clinical evidence of fluid overload, either predialysis (0.96 +/- 0.16) or postdialysis (0.92 +/- 0.16); p = 0.07 and 0.36 respectively. Blood Pressure: Mean +/- standard deviation systolic blood pressure (BP) was 111.9 +/- 18.2 mmHg and diastolic BP was 63.3 +/- 11.9 mmHg, with only 4 (7%) patients having a systolic BP > 140 mmHg and 1 (2%) having a diastolic BP > 80 mmHg. Median number of antihypertensives was 1 per day. Blood pressure control and ECW/ICW ratio were similar in those with sodium removal >120 mmol/day compared to those with sodium removal < or =120 mmol/day (p = 0.39 for SBP, p = 0.70 for diastolic BP, p = 0.24 for ECW/ICW).

CONCLUSIONS

We have shown that good blood pressure and volume control is achievable in a large contemporary APD population with liberal use of icodextrin and avoidance of long daytime glucose-based dwells. Neither low nor high sodium removal was associated with more frequent hypertension or volume expansion.