Cj. Nelson et al., Enhancement of the contact hypersensitivity reaction by acute morphine administration at the elicitation phase, CLIN IMMUNO, 93(2), 1999, pp. 176-183
The present study investigated the effects of morphine on the irritant cont
act sensitivity (ICS) and contact hypersensitivity (CHS) reaction. ICS was
induced by croton oil application on the pinnae of naive rats, Morphine inj
ected prior to croton oil application did not affect the ICS response when
assessed by measurements of pinnae thickness, CHS was induced by applying t
he antigen 2,4-dinitro-1-fluorobenzene (DNFB) to the pinnae of rats sensiti
zed to DNFB. Rats received an injection of morphine prior to either initial
antigen exposure (sensitization) or antigen reexposure (challenge). Morphi
ne prior to challenge, but not sensitization, resulted in a pronounced enha
ncement of the CHS response as measured by pinna thickness. Quantitative PC
R also showed increased IFN-gamma mRNA levels in the inflamed tissue of mor
phine-treated rats. Naltrexone blocked the morphine-induced enhancement of
the CHS response. The differential effects of morphine suggest that opioids
have a more pronounced effect on in vivo immune responses that involve imm
unological memory. (C) 1999 Academic Press.