Immunoglobulin M production and immunosuppression in trypanosomiasis: a linking hypothesis

Vaccination against trypanosomiasis: can it be done or is the trypanosome truly the ultimate immune destroyer and escape artist?

To date, human African trypanosomiasis (HAT) still threatens millions of people throughout sub-Sahara Africa, and new approaches to disease prevention and treatment remain a priority. It is commonly accepted that HAT is fatal unless treatment is provided. However, despite the well-described general symptoms of disease progression during distinct stages of the infection, leading to encephalitic complications, coma and death, a substantial body of evidence has been reported suggesting that natural acquired immunity could occur. Hence, if under favorable conditions natural infections can lead to correct immune activation and immune protection against HAT, the development of an effective anti-HAT vaccine should remain a central goal in the fight against this disease.<br /> In this review, we will (1) discuss the vaccine candidates that have been proposed over the past years, (2) highlight the main obstacles that an efficient anti-trypanosomiasis vaccine needs to overcome and (3) critically reflect on the validity of the widely used murine model for HAT.

Interaction of nutrition and infection: effect of zinc deficiency on resistance to Trypanosoma musculi

1. Zinc deficiency was studied in mice infected with Trypanosoma musculi. 2. In all dietary groups, the infected animals consumed more food and gained more weight than the uninfected controls. 3. In all studies, at the peak of parasitemia, the zinc-deficient animals showed three times the number of trypanosomes as that of the complete and pair-fed mice. 4. The average coefficients of variation in body lengths of T.musculi cells indicated that the formation of the reproductive-inhibiting antibody (ablastin) occurred later in zinc-deficient animals compared to animals fed complete diets. The degree and duration of parasitemia in the zinc-deficient animals indicated a delay in the synthesis of the terminal lytic antibody. 5. Irrespective of diets, severe depression in the primary and secondary antibody responses to in vivo immunization of sheep erythrocytes was observed in infected animals over non-infected controls.

The pathogenesis of sleeping sickness

Although the clinical and pathological features of sleeping sickness have been well recognized since the beginning of the century, we still have very little idea about how these changes are brought about. A convincing role for a trypanosome-derived toxin has yet to be established and it is probable that most tissue damage results from an immunopathological reaction. An immediate type hypersensitivity reaction might account for the pruritus and urticaria sometimes encountered in patients with the infection. Autoantibodies are produced by patients with sleeping sickness but it has not been established that these can cause tissue damage. Similarly, although high levels of immune complexes are found in patients with sleeping sickness, it has yet to be clearly established that these damage the brain or heart. The dominant pathological event in sleeping sickness is B lymphocyte proliferation, first within the lymph nodes and then within the brain and meninges, and this response may lead to tissue damage in some way which has not yet been identified. B lymphocyte proliferation could result from the action of a trypanosome-derived mitogen or from interference with T lymphocyte control over B lymphocyte function.

Mitogenic activity of an extract of Trypanosoma gambiense

An extract obtained by repeated freeze/thawing of a freshly isolated strain of Trypanosoma gambiense caused stimulation of lymphocytes obtained from healthy adult donors and from cord blood. The active factor had some stimulatory effect on purified B and T lymphocytes and in two of five subjects increased IgM production by lymphocytes cultured in vitro. A trypanosome-derived mitogenic factor may play some part in the pathogenesis of the hypergammaglobulinaemia characteristic of African trypanosomiasis.

Free fatty acids, complement activation, and polyclonal B-cell stimulation as factors in the immunopathogenesis of African trypanosomiasis

Human and animal forms of African trypanosomiasis are characterised by sustained hypocomplementaemia, gross hypergammaglobulinaemia M, and profound immunosuppression. It is suggested that this hypocomplementaemia is probably due to the action of a trypanosome-derived complement-activating factor and that the elevated IgM levels may be the combined result of this decomplementation, together with a subsequent failure of the normal IgM-to-IgG antibody switch mechanism and polyclonal B-lymphocyte activation by a trypanosome-generated mitogen. The immunosuppression in this disease may be a result of the collective immunosuppressive effects of trypanosome-derived immune-modulating free fatty acids, polyclonally stimulating B-cell mitogen, and complement-activating factors.

The immune response of zebu cattle infection with Trypanosoma congolense and T. vivax

Zebu cattle were infected with Trypanosoma congolense and T. vivax and changes in the levels of serum immunoglobulins were measured during infection and after treatment. Increases in the levels of IgM occurred within 14 days of infection coincidentally with the first appearance of trypanosomes in the peripheral blood. IgM levels rose to 2-10 times preinfection levels and remained high until the animals were treated with diminazene aceturate. Levels then declined to approximately pre-infection levels within 25 days. IgG levels showed little change. In one animal infected with T. congolense which died of trypanosomiasis, there was an initial increase in IgM levels but subsequently both IgM and IgG levels declined until the animal died. The neutralizing activity of whole serum, and serum IgM and IgG fractions from an ox infected with T. congolense were examined. High levels of neutralizing antibodies against trypanosomes isolated on the eighth day after infection were found in sera collected 12-29 days after infection. Most of the antibody activity was located in IgG fractions which showed a peak in neutralizing activity between day 17 and 22. IgG fractions of the sera showed only slight antibody activity.