Objective: To investigate whether neonatal polymorphonuclear (PMNs) cells are capable to produce heat shock proteins(hsps) after exposure to hyperthermia, as do the adult PMNs after exposure to different stresses.

Design: We studied PMNs from 15 neonates and 15 adults. Hsps were detected in these cells: 1) by a direct qualitative method(Western blotting) in PMNs exposed to a high temperature (43 °C) and 2) by an indirect method [measurement of superoxide (O2-) which is known to be suppressed by hsps]. The generation of O2- was measured by the superoxide dismutase-inhibitable reduction of ferricytochrome C in a) PMNs exposed to a neutral temperature (37 °C) b) PMNs exposed to a high temperature (43 °C) c) PMNs which initially were exposed to 43 °C, afterward they were allowed to “recover” (for two hours in a neutral temperature) and subsequently they were exposed to a second heat stress (43 °C).

Results: In both neonatal and adults PMNs exposed to heat stress we have detected hsps. Heat stress (43 °C) suppressed the superoxide generation in both neonatal (p<0.0001) and adult PMNs(p<0.0001). However, when the preheated PMNs were exposed to a second heat stress, they did not inhibited the superoxide generation as did during the first heat exposure (p between first and second heat exposure <0.0001 for adults and <0.0001 for neonates). This means that preheated PMNs exhibited thermotolerance.

Conclusion: Neonatal PMNs are able to produce hsps. This production seems to protect the neonatal cells from insults caused by high temperature and consequently other stresses.