Products of fourth-stage larvae of Oesophagostomum dentatum induce proliferation in naive porcine mononuclear cells

Infection of pigs with Oesophagostomum dentatum is a major cause of economi c losses in pig productions. Whether infection with this nematode results i n a protective immunity is still in debate and information about immune-mod ulating properties of O. dentatum are lacking. The present study investigat ed the question whether products of O. dentatum larvae modulate the prolife rative response of porcine blood mononuclear cells (poMNC) in vitro. The po MNC of naive and O. dentatum-infected pigs were cultured for 72 h in the pr esence of products (total homogenates and culture supernates) derived from third- (L-3) and fourth-stage larvae. (L-4) of O. dentatum. Numbers of vita l cells and blast-transformed cells were determined flow cytometrically. No larvae product induced an accelerated death of poMNC in vitro. In contrast , products of L-4 (but not L-3) significantly increased the numbers of vita l poMNC in vitro (up to 187%). In addition, L-4 products (homogenates and s upernates, 0.1-10 mug/ml) but not those of L-3 induced significant blastoge nesis of poMNC. This was seen with poMNC from naive and from O. dentatum-in fected animals. In spite of these effects, the larvae products were not abl e to modulate die mitogen-induced (Concanavalin A) poMNC proliferation of n aive and infected animals. In summary, larvae of O. dentatum contain and se crete products with potential immunomodulatory capacity for porcine periphe ral blood mononuclear cells. The differential effects of L-3 and L-4 indica te that the parasite alters its set of immunomodulatory substances during i ts development. This has to be considered in further studies and may help t o identify the mediators involved.