Abstract 98

Background: Activated polymorphonuclear leukocytes (PMN) are extremely rigid compared to passive PMN. They may lead to obstruction of narrow vessels (e.g. in septicemia) and contribute to ischemic organ injury. Since PMN in neonates show functional defects in the defence against bacterial infections compared to PMN in adults (impaired adherence, diminished phagocytosis, lower bactericidal activity, decreased chemotaxis) we studied the deformability of PMN in vitro after activation with N-formyl-methionyl-leucyl-phenylalanine (FMLP). interleukin-8 (IL-8) and tumor-necrosis-factor (TNF-α) and the effect of pentoxifylline and enoximone to prevent activation of PMN.

Subjects: Blood samples from 20 healthy neonates and 20 non-smoking healthy male adults were studied.

Measurements: The elapsed time for aspiration of PMN from full-term neonates and adults into a micropipette with an internal diameter of 5µm and the transit times for the passage of neutrophils through 8µm filter pores of a cell transit analyzer were determined as parameters of cell deformability.

Results: Passage times of activated PMN were significantly increased (p<0.05) compared to passive PMN. IL-8 and TNF-α increased passage times of PMN by about 2.5 times, FMLP by about 4 times. The PMN of term neonates showed neither differences in the number of activated cell nor in whole cell deformability compared to PMN in adults. The addition of pentoxifylline (PTX) to PMN activated with IL-8 or TNF-α increased the deformability by 30 to 40 % (p<0.05). The deformability of PMN activated with FMLP increased with the addition of PTX or enoximone by 40 to 50 %(p<0.05). PMN in neonates and adults showed a similar behaviour after treatment with PTX and enoximone.

Conclusions: The present results suggest, that despite of functional differences between the PMN in neonates and adults there are no differences in the rate of activation, the deformability of activated PMN and in the response of activated PMN to deactivate in the presence of PTX and enoximone between full-term neonates and adults. Activation of PMN might lead to a significant increase in the precapillary resistance. This might be partially corrected by treatment with pentoxifylline and enoximone.