We have reported the production of several hybridoma lines secreting monoclonal antibodies recognizing antigens of the blood forms of a rodent malaria parasite, Plasmodium yoelii yoelii1,2. Line WIC 25.77 secretes an IgG2a (antibody 25.77) which reacts specifically with merozoites in the indirect immunofluorescence (IIF) assay, and which was protective on passive transfer. Another of the hybridoma lines, WIC 25.1, secretes an IgG2a (antibody 25.1) which reacts with an antigen apparently associated with the membranes of schizonts, but this antibody was not protective on passive transfer. We have used our monoclonal antibodies to identify and purify antigens of P. y. yoelii, and we report here that mice immunized with either a 235,000 apparent molecular weight (MW) merozoite-specific protein or a 230,000 MW schizont protein and its proteolytic derivatives were protected against infection with P. y. yoelii.

Immunization against blood-stage rodent malaria using purified parasite antigens.

Although it is difficult to draw any sweeping conclusions that would be applicable to all helminth infections, the main features that are emphasized in this review may be summarized briefly. Pathogenic helminths, although extremely diverse in structure and behaviour, have one common feature, namely that they present to the host's defenses large, non-phagocytosable surfaces. Because of this, they are susceptible to a range of effector mechanisms differing either quantitatively or qualitatively from those that are active against other parasites or against normal or abnormal host cells. As an extreme example, the various types of cytotoxic lymphocyte, with one interesting exception, are inactive against helminths. Instead, helminth infections are characterized by high IgE responses and increased numbers of circulating eosinophils. Such eosinophils are activated, and show a marked capacity to kill a variety of target helminths in vitro. Further activation may occur in response to mast cell mediators released as a result of IgE-dependent degranulation; and IgE, as well as IgG and complement, can mediate eosinophil attachment and killing. It may therefore be suggested that the eosinophil/IgE/mast cell axis represents a powerful host defense against helminth infections. IgE can also mediate macrophage-dependent killing of several helminths, a process which involves a functional change in the macrophage, resembling activation. Although eosinophil-mediated and IgE-dependent macrophage-mediated effects are particularly potent, other effector cells are not excluded: in certain circumstances, neutrophils and conventionally activated macrophages may be equally or more effective. Neutrophils appear to act solely by oxidative killing mechanisms, whereas degranulation and the release of toxic granule contents is equally or more important in eosinophil-mediated damage. Different stages of different helminths vary in their degree of susceptibility to different mechanisms. Eosinophils appear to be somewhat less active than neutrophils against ensheathed nematodes, whereas trematodes and exsheathed nematodes are highly susceptible to eosinophil attack. In many experimental helminth infections, studies in vivo suggest a role for antibody-dependent cell-mediated immune effector mechanisms. The identity of the effector cell is difficult to establish because of a lack of techniques for specific manipulation of individual cell types, but histological studies frequently point to a strong eosinophil or macrophage involvement. The development and analysis of in vitro assays allows the study of immune effector mechanisms in man.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell-mediated damage to helminths.

An amazing number of antifungal agents are found within the group of azole-containing compounds. A great number are breakthroughs in anti-fungal therapy in both human and veterinary medicine, and they show excellent activity against phytopathogenic fungi. Structural formulae of some imidazole and triazole derivatives are shown in Figures 12-1 and 12-2.

Biochemical Targets for Antifungal Azole Derivatives: Hypothesis on the Mode of Action

Cytochrome P450s (P450s) are subject to inhibition/inactivation by various chemically diverse agents, which may interact directly or indirectly with either the P450 prosthetic heme or the protein moiety or with both moieties. This inhibition is clinically relevant, as it can block physiological pathways as well as result in therapeutically significant beneficial or adverse effects and clinically relevant drug–drug interactions. Herein, we discuss the various chemical agents and their chemical mechanisms that lead to such reversible, quasi-irreversible, or irreversible inhibition of these enzymes. We note that such inhibition targeted at P450-dependent physiological and/or pathological processes has been ingeniously and effectively harnessed not only in the design and development of clinically relevant therapeutic agents but also of fungicides, insecticides, and herbicides.

Inhibition of Cytochrome P450 Enzymes

The modes of action of fasciolicides are described. Closantel and other salicylanilides interfere with energy metabolism by uncoupling oxidative phosphorylation in the fluke. Other fasciolicides are believed to have a metabolic action-halogenated phenols (via uncoupling) and clorsulon (via inhibition of glycolysis)-but direct evidence is lacking. Benzimidazoles (in particular, triclabendazole) bind to fluke tubulin and disrupt microtubule-based processes. Diamphenethide inhibits protein synthesis in the fluke. Other potential drug actions may contribute to overall drug efficacy. In particular, a number of fasciolicides-salicylanilides, phenols, diamphenethide-induce a rapid paralysis of the fluke, so their action may have a neuromuscular basis, although the actions remain ill-defined. Resistance to salicylanilides and triclabendazole has been detected in the field, although drug resistance does not appear to be a major problem yet. Strategies to minimize the development of resistance include the use of synergistic drug combinations, together with the design of integrated management programmes and the search for alternatives to drugs, in particular, vaccines.

R. B. Podesta

Papers

The Host-Invader Interplay