Natural resistance to animal parasites

Complement is a rat natural resistance factor to amoebic liver infection

Amoebiasis is a parasitic disease caused by Entamoeba histolytica. This illness is prevalent in poor countries causing 100,000 deaths worldwide. Knowledge of the natural resistance mechanisms of rats to amoebic liver abscess (ALA) development may help to discover new pathogenic factors and to design novel therapeutic strategies against amoebiasis. In this work, histologic analyses suggested that the complement system may play a central role in rat natural resistance to ALA. E. histolytica trophozoites disappeared from rat liver within 6 h post-infection with minimal or no inflammatory infiltrate. In vitro findings indicate that rat complement was lethal for the parasite. Furthermore, hamsters became resistant to ALA by intravenous administration of fresh rat serum before infection. The amoebicidal potency of rat complement was 10 times higher than hamster complement and was not related to their respective CH50 levels. The alternative pathway of complement plays a central role in its toxicity to E. histolytica since trypan blue, which is a C3b receptor inhibitor, blocks its amoebicidal activity. These results suggest that amoebic membrane affinity, high for C3b and/or low for Factor H, in comparison with the hamster ones, may result in higher deposition of membrane complex attack on parasite surface and death.

Sexual reproduction as an adaptation to resist parasites (a review)

Darwinian theory has yet to explain adequately the fact of sex. If males provide little or no aid to offspring, a high (up to 2-fold) extra average fitness has to emerge as a property of a sexual parentage if sex is to be stable. The advantage must presumably come from recombination but has been hard to identify. It may well lie in the necessity to recombine defenses to defeat numerous parasites. A model demonstrating this works best for contesting hosts whose defense polymorphisms are constrained to low mutation rates. A review of the literature shows that the predictions of parasite coevolution fit well with the known ecology of sex. Moreover, parasite coevolution is superior to previous models of the evolution of sex by supporting the stability of sex under the following challenging conditions: very low fecundity, realistic patterns of genotype fitness and changing environment, and frequent mutation to parthenogenesis, even while sex pays the full 2-fold cost.

Immunological and nonimmunological control of severity of Trypanosoma musculi infections in C3H and C57BL/6 inbred mice

Studies concerned with the mechanisms responsible for relative resistance or susceptibility of strains of inbred mice to Trypanosoma musculi infections are presented. Treatment with 400 rads of ionizing radiation, silica dust, or trypan blue (reticuloendothelial blocking agents) rendered C3H mice unable to control the initial maximum level of parasite growth, and the mice died of overwhelming infections. In contrast, similarly treated C57BL/6 (relatively resistant) mice controlled initial trypanosome growth as well as controls; however, the duration of infection, preceding eventual cure, was approximately doubled. Combined treatment with trypan blue and 400 rads of radiation resulted in much higher initial levels of infection in C57BL/6 mice, and about half of the mice died; the remaining mice eventually recovered after a prolonged course of infection. These results indicate that a nonimmunological mechanism, which controls initial infection, and an immunological mechanism cooperate to limit T. musculi infections in normal mice. We present results that suggest that both mechanisms are less effective in C3H than in C57BL/6 mice. The initial control of infection presumably reflects the activity of some type(s) of phagocytic effector cell; we show, however, that the initial control of infection is not an attribute of the liver Kupffer cells. Identification and characterization of the cells capable of controlling initial infection could lead to procedures for enhancing their function and, thus, to enhanced resistance to, and elimination of, trypanosome infections.

Cooperative action of complement component C3 and phagocytic effector cells in innate murine resistance to Trypanosoma lewisi

Mice display strong natural resistance to the rat-specific Trypanosoma lewisi. Intravenously injected intact T. lewisi parasites were eliminated by mice within 18 to 24 h. In comparison, "nude" T. lewisi organisms lacking the surface coat were rapidly and totally cleared from the bloodstream within 2 h postinoculation. Similarly, in vitro-cultivated trypanosomes were readily eliminated by mice with the conspicuous absence of a lag phase. Elimination of nude T. lewisi, like that of intact trypanosomes, required murine complement component C3. Splenectomy of mice did not affect their ability to eliminate T. lewisi. However, C3 depletion with cobra venom factor rendered splenectomized mice susceptible to this rat trypanosome; in these mice, T. lewisi established prolonged and frequently fatal infections. Beige mice were able to efficiently eliminate T. lewisi. But combined treatments of beige (bg/bg) and heterozygous (bg/+) mice with cobra venom factor and silica dust, or normal rat serum and silica dust, incapacitated the natural resistance of these mice to T. lewisi. Such combined treatments of beige and control mice resulted in fulminating parasitemias and death of the animals. Altogether, the results of the present studies indicate that T. lewisi elimination by mice requires the following: exposure of C3 acceptors on the surface of the parasites; activation of murine C3, probably via the alternative complement pathway; and destruction of the C3b-coated parasites by their interaction with C3b receptor-bearing, phagocytic effector cells that are abundant in the spleen and sensitive to silica dust.

Genetic and sex-related differences in the structure of submandibular glycoconjugates

Structures of oligosaccharides in submandibular glycoproteins were evaluated in situ. Sections of fixed paraffin-embedded glands from rats, mice, hamsters, sheep, and man were stained with a battery of lectins conjugated to horseradish peroxidase in conjunction with other methods, such as digestion with sialidase with or without prior saponification and/or periodate oxidation. Secretory glycoproteins showed a characteristic lectin binding pattern for each genus. Sialoglycoconjugates were detected in acinar cell secretions in all genera except the rat but differed with respect to the linkage of sialic acid to penultimate beta-galactose or alpha-N-acetylgalactosamine. Species and strains of mice showed minor differences in the structure of secretory glycoproteins. Sexes differed similarly in some but not other mouse species. Individual differences were seen in human glands, where oligosaccharide structure varied in relation to ABO blood group. In some species, heterogeneity in glycoprotein structure was observed among morphologically similar cells within a gland. Differences in the structure of salivary secretions between genera and between humans of different ABO blood type and secretor status substantiate biochemical and histochemical findings. The results showing species, sex, and individual differences in mice and heterogeneity in acinar cells in several species suggest a greater degree of genetic and perhaps hormonal influence on the synthesis of salivary glycoproteins than has previously been recognized.