Schistosoma mansoni: relationship between cercarial production levels and snail host susceptibility.

Two populations of Biomphalaria glabrata snails differing slightly in their susceptibility to Schistosoma mansoni infection showed dramatic differences in cercarial output per snail. Exposed to five or more miracidia, snails from a group with a 90-100% susceptibility rate (Group A) produced nearly twice the number of cercariae as those from a group with a 70-80% susceptibility rate (Group B). Exposure of individual snails to known numbers of miracidia resulted in higher numbers of primary (mother) sporocysts in Group A snails than in Group B snails. However, monomiracidial exposure of snails from both groups resulted in equivalent numbers of cercariae produced per positive snail, indicating that, once established, all primary sporocysts possess a similar reproductive potential. Morphometric analysis of serially sectioned 9-day-old primary sporocysts supported this conclusion; the size of the primary sporocysts and the size and numbers of secondary (daughter) sporocysts within each primary sporocyst were comparable in snails from both groups. The data indicate cercarial production in this system is regulated prior to, and/or during, early development of the primary sporocyst.

[The use of monoclonal antibodies in plant production]. / Toepassing van monoclonale antilichamen in de plantaardige produktie.

Due to the high specificity of monoclonal antibodies (MCAs) the most important application of MCAs in the plant production may be diagnosis. Specific MCAs have been produced against plant pathogens including viruses, bacteria, fungi and nematodes and against plant substances. In general, however, MCAs are still less suitable than polyclonal antisera for application as diagnostic tools in plant extracts.

Antigenic variation in African trypanosomiasis: a memorandum.

After reviewing the present knowledge on antigenic variation of the trypanosomes of the Trypanosoma (Trypanozoon) brucei species, this Memorandum discusses the relevance of this phenomenon to the possible development of new tools for trypanosomiasis control.As antigenic variation is related to protective immunity and immunopathology, it is of crucial importance for the feasibility of vaccine development and for treatment principles. It is also of interest as a model for understanding antigenic variation occurring during infections with Plasmodium knowlesi, Babesia, and others. Recent methods will permit in depth studies on the antigenic repertoire, the significance of basic antigens, and on the homogeneity of trypanosome populations. For epidemiological purposes, characteristic patterns of variation can be used for strain typing.As regards the basic mechanism of variation, a better insight is required on the molecular structure of the variant antigens. Various methods have so far indicated that they are glycoproteins with a long polypetide chain with 600 amino acids and 15-30 monosaccharide units.The process of variation may be generated by pre-existing genetic information, recombination, or mutation.The stimulus to change variants probably derives, directly or indirectly, from the host immune response, but may also be associated with other environmental factors.The possible relation to acquired resistance, innate immunity, and host specificity, as well as the differences in severity of infection occurring amongst the same host species, are outlined. Histopathological and serological findings are considered in the light of the effect antigenic variation may have on the development of immunopathological lesions.A series of recommendations is included.