Monocyte normal immune response to LPS stimulation

Introduction

Monocyte stimulation with LPS has been used to evaluate adequacy of immune response in immunocompromised patients (monocyte deactivation) with severe sepsis. The aim of the study was to investigate the dose response curve of maximum monocyte TNF-α production after LPS stimulation.

Methods

Peripheral blood was obtained from 16 volunteers and the absolute number of monocytes per 100 μl was measured. The same quantity was stimulated by different doses (50, 100, 250, 500, 1000 pg) of LPS for 4 hours. TNF-α levels were measured at baseline and after stimulation and were converted per monocyte. Stimulation with 500 pg of LPS was found to best stimulate monocytes. Then, 100 μl of the same specimens were stimulated with 500 pg of LPS for 4, 8 and 24 hours.

Results

Baseline levels of TNF-a were undetectable. After different doses of LPS stimulation for 4 hours TNF-a levels were as follows:

• (a) 50 pg/ml LPS: 995.8 ± 60.6 totally and 9.5 ± 1.6/monocyte,

• (b) 100 pg/ml LPS: 1084.6 ± 62.2 totally and 10.8 ± 1.9/monocyte

• (c) 250 pg/ml LPS: 1214.7 ± 73.1 totally and 13.9 ± 2.6/monocyte

• (d) 500 pg/ml LPS: 1307.1 ± 68.4 totally and 16.6 ± 2.8/monocyte

• (e) 1000 pg/ml LPS: 1214.2 ± 67.2 totally and 16.8 ± 2.1/monocyte

Timeframe for TNF-α production after stimulation with 500 pg of LPS is shown in Table 1

Table 1

Conclusions

Maximum monocyte TNF-α production was observed after stimulation with 500 pg of LPS which was not statistically different compared to 1000 pg. Also, maximum response with 500 pg of LPS was observed after 24 hours of stimulation. These findings are in contrast with the literature which suggests stimulation using 100 pg of LPS for 4 hours for the evaluation of monocyte immune competency.