Surface antigen cross-linking triggers forced exit of a protozoan parasite from its host.

Abstract

We used the common fish pathogen Ichthyophthirius multifliis as a model for studying interactions between parasitic ciliates and their vertebrate hosts. Although highly pathogenic, Ichthyophthirius can elicit a strong protective immune response in fish after exposure to controlled infections. To investigate the mechanisms underlying host resistance, a series of passive immunization experiments were carried out using mouse monoclonal antibodies against a class of surface membrane proteins, known as immobilization antigens (or i-antigens), thought to play a role in the protective response. Such antibodies bind to cilia and immobilize I. multifiliis in vitro. Surprisingly, we found that passive antibody transfer in vivo caused rapid exit of parasites from the host. The effect was highly specific for a given L multifiliis serotype. F(ab)2 subfragments had the same effect as intact antibody, whereas monovalent Fab fragments failed to protect. The activity of Fab could, nevertheless, be restored after subsequent i.p. injection of bivalent goat anti-mouse IgG. Parasites that exit the host had detectable antibody on their surface and appeared viable in all respects. These findings represent a novel instance among protists in which protective immunity (and evasion of the host response) result from an effect of antibody on parasite behavior.

An Overview of the Immunological Defenses in Fish Skin

“…Antibodies in cutaneous mucus and skin of teleosts play a critical role in the protective host defence against surface infections [224,225] and were reported to be similar, but not identical, to serum IgM [218,226]. It is thought that the IgM antibodies possess a limited antigen spectrum in fishes.…”

“…Usually the amounts found are extremely small compared to the amounts of IgA in mammalian secretions and are temperaturedependent. More concretely, IgM levels increase when there is an increase in water temperature [218,[224][225][226][227].…”

Therapeutic and prophylactic effects of a protective monoclonal antibody (MAb-001) against the pathogenic haemoflagellate Cryptobia salmositic

“…of 10 MAb-001-injected fish had no detectable complement-fixing antibodies against Cryptobia salmositica while 10 of 10 fish (injected with saline) had antibodies which lysed parasites under in vitro conditions. Though murine monoclonal antibodies against Ichthyophthirius mulfifiliis provided complete protection against infection in channel catfish, the mechanism of protection is believed to be different; the antibody when attached to the parasites forces the parasite to leave the host (Clark et al 1996). …”

Toltrazuril (Baycox<SUP>®</SUP> vet.) in feed can reduce <I>Ichthyophthirius multifiliis</I> invasion of rainbow trout (Salmonidae)

“…The inflicted pathology is often referred to as the white spot disease. Although the immune response in fish against these skin parasites offers some protection (Clark et al 1996, Buchmann et al 2001 formaldehyde and copper sulphate may soon be banned for aquaculture usage due to their adverse environmental and health effects. Therefore farmers need legal and licensed products for control of the disease.…”

“…The inflicted pathology is often referred to as the white spot disease. Although the immune response in fish against these skin parasites offers some protection (Clark et al 1996, Buchmann et al 2001, Alishahi and Buchmann 2006, Dickerson 2006, Xu et al 2006) a number of mechanical (Shinn et al 2009) or chemical measures must be applied in order reduce morbidity in aquaculture enterprises. Fish farmers are currently using a series of auxiliary substances such as formaldehyde, copper sulphate, and peracetic acid (Straus andMeinelt 2009, Bruzio andBuchmann 2010) or sodium percarbonate (Heinecke and Buchmann 2009) for control of white spot disease through continuous treatment of Ich-infected water.…”