Eosinophil influx to the nasal airway after local, low-level LPS challenge in humans

BACKGROUND

Recent observations show that atopic asthmatic subjects have increased sensitivity to respirable endotoxin (or LPS) compared with normal persons. In vitro studies demonstrate that LPS enhances eosinophil survival. These observations suggest that the effects of inhaled LPS in asthmatic subjects may include increases in the number of airway eosinophils.

OBJECTIVE

We sought to determine whether low-level nasal LPS challenge causes an increase in eosinophil numbers in the nasal airways of atopic or normal subjects.

METHODS

Sixteen volunteers (10 atopic asthmatic subjects and 6 normal subjects) underwent 2 nasal challenge sessions. In one session, one nostril was challenged with saline and the other with 0. 1 microg of LPS. During the second session, 0.3 microg and 1.0 microg of LPS was delivered to each nostril, respectively. Nasal lavage fluid was obtained from each nostril before challenge, as well as 4 and 24 hours after challenge, and examined for the percent of total cells that were eosinophils and neutrophils, as well as cytokine levels.

RESULTS

LPS (1.0 microg) increased the percent of eosinophils in nasal lavage fluid 4 hours after challenge in atopic subjects only. There was also a correlation between constitutive nasal GM-CSF and eosinophil response to LPS in atopic subjects.

CONCLUSION

LPS challenge increases eosinophils in the airways of atopic subjects.

Carboxyhemoglobin and brain blood flow in humans

It has been shown that with increased carboxyhemoglobin (COHb) and associated decrease in blood oxygen-carrying capacity, a compensatory increase in brain-blood flow (BBF) develops. The BBF response in humans has been shown to be quite variable. Two experiments were conducted in which humans were exposed to sufficient carbon monoxide (CO) to produce COHb levels up to 18.4%. BBF was measured by the method of impedance plethysmography. The first was a pilot study in which BBF in 14 men was studied after transient exposure to various concentrations of CO in air. BBF increased as a function of COHb but not to the same extent (or at all) in some subjects. In a confirmatory experiment with 12 men, BBF was measured once per h during a 4-h experiment. All 12 subjects received CO. The variation of the BBF response among subjects was large and statistically significant whereas the variation over time was not significant. Thus it appears that the magnitude of the BBF response is unique for a given subject and differs across subjects. These results may help predict CO-induced behavioral decrements in future studies if subjects whose BBF response to COHb is small or absent are also more susceptible to impairment by acute CO exposure.