Molecular Basis of Host‐Parasite Relationship: Towards the Definition of Protective Antigens

Abstract

In spite of some remarkable progress in our understanding of the immune response to parasites and in the molecular cloning of dozens of genes encoding for potentially protective proteins, no definitive step has yet been made towards operational vaccines against major human parasitic diseases. The reasons for our present failures are no longer attributable to the lack of appropriate tools but rather to our rather primitive knowledge of the basic mechanisms governing host-parasite relationship. Mainly on the basics of our personal observations, we have attempted to review and discuss some of the prominent factors in host-parasite interactions, such as molecular mimicry, phyletic convergence, molecular mechanisms of infectivity and lures of cell communication. In many respects, the development of efficient vaccines applicable to humans appears closely dependent on a better understanding of the basic biological mechanisms underlying the natural history of parasitic diseases. In this context, the development of new concepts regarding the definition of potentially protective antigens based on the study of non-surface molecules, cross-reactive stage antigens and antibody isotype selection might represent promising alternatives.

Comparative Antigen Analysis of Different Life Stages of <i>Schistosoma mansoni</i> by Crossed Immunoelectrophoresis

“…It should be mentioned that, tak ing into account also the antigen components noted as not identified (see table 1), the number of antigens shared by adult worm and egg totalled seventeen and by adult worm and cercaria nineteen. These findings arc principally in accordance with results published by Capron et al [1] and the phenomenon of antigens shared between different life stages and their possible participation in concomitant immunity has been put forward by Capron and Dessaint [20], More recently, immunoprécipitation and absorption experiments have shown that none of the adult tegumental mem brane antigens is detectable in S. mansoni eggs [21], suggesting that the ten SAWA antigens, including the MDH, which in the present study were shown to be shared between adult worm and egg could be nonsurface (adult schistosome) antigens. So, for instance, the MDH component has been shown to be localized in the cellular layer of the cecum of adult schisto somes [10].…”

“…It is worth noting that the presence of stage specif ic antigens may imply a survival advantage to the par asite and that such antigens would not be the prime target for the immune defence mechanisms of the host. Therefore the search for potentially protective antigens should rely more on the characterization of cross-reacting molecules than on stage specific anti gen components [20].…”

Protein tyrosine kinases as new potential targets against human schistosomiasis

“…Massive trapping of eggs into host organs initiates the formation of inflammatory granulomas leading to hepatic tissue destruction. Such a successful and prolific schistosome life cycle has been shown to be dependent on the adaptive molecular dialogue that exists between the parasite and the host (5,6) and the receipt by the parasite of host signals (hormones, growth factors) that could control actively cell proliferation and differentiation processes in schistosomes. (7)(8)(9)(10)(11)(12) In this context, diverse molecular pathways dependent on kinase signalling have been described in schistosomes and shown to be involved in hostparasite relationships.…”

Paediatric oncology in developing countries

“…In addition, numerous viral and parasitic antigens are known to release cytokines inhibiting monocyte/macrophage and lymphocyte proliferation and expression of interleukin-2 receptors [9].…”