A suppressor T-cell defect in tropical splenomegaly syndrome

Burkitt's Lymphoma

Endemic Burkitt's lymphoma (BL) remains the most prevalent pediatric cancer in sub-Saharan Africa even though it was the first human cancer with a viral etiology described over 50 years ago. Epstein-Barr virus (EBV) was discovered in a BL tumor in 1964 and has since been implicated in other malignancies. The etiology of endemic BL has been linked to EBV and Plasmodium falciparum malaria co-infection. While epidemiologic studies have yielded insight into EBV infection and the etiology of endemic BL, the modulation of viral persistence in children by malaria and deficits in EBV immunosurveillance has more recently been reified. Renewed efforts to design prophylactic and therapeutic EBV vaccines provide hope of preventing EBV-associated BL as well as increasing the ability to cure this cancer.

The importance of the spleen in malaria

There are several malaria vaccine candidates at various stages of development. Many of these target blood stages of Plasmodium falciparum. The spleen is a key site for removal of parasitized red blood cells, generation of immunity and production of new red blood cells during malaria. This article describes how all of these processes are modified following infection, and suggests that until we fully understand how these processes function and are modulated by infection, appropriate malaria vaccine design and delivery will be extremely difficult to achieve.

P. falciparum invasion of human red cells and cytoadherence to endothelial cells is dependent upon a parasite produced glycosidase

This report describes biochemical and immunological evidence that P. falciparum produces an neuraminidase-like activity on invasion into the human red cell. The enzyme-like activity modifies the surface of glycophorin A on the infected red cell membrane to prevent further invasion of other merozoites, as well as to enhance the binding capabilities of the red cell to the host's endothelial cells (EC).

The sickle-cell trait modifies the intensity and specificity of the immune response against P. falciparum malaria and leads to acquired protective immunity

It is proposed that the in vivo mechanism of protection against falciparum malaria in individuals of the Hb AS genotype is not due solely to the adverse influence of Hb AS erythrocytes on the intraerythrocytic growth and development of P. falciparum. Instead, the simple physiological effect of Hb S on parasite growth appears to trigger an in vivo process of enhancement of the intensity and/or specificity of the host immune response, leading to acquired protective immunity, in a process simulating vaccination. Testing the hypothesis may lead to the identification of plasmodial antigens that induce protective responses in the human host and distinguish them from non-protective, immunosuppressive or decoy antigens that promote parasite survival. This may ultimately help in the selection of candidate antigens for a malaria blood-stage vaccine.

Antibody-mediated killing of suppressor T lymphocytes as a possible cause of macroglobulinemia in the tropical splenomegaly syndrome

To investigate the pathogenesis of macroglobulinemia in the tropical splenomegaly syndrome (TSS), we assessed the functional activity of B lymphocytes and T cell subsets in a pokeweed mitogen-driven assay of immunoglobulin synthesis. Mononuclear cells from patients with TSS produced more IgM than cells from village or from distant controls. This appeared to result from a decrease in the number and/or activity of suppressor T cells of the T8+ phenotype. The lack of functional suppressor T lymphocytes was associated with the presence in sera from patients with TSS of IgM antibodies that specifically killed T8+, 9.3-, 60.1+ T cells from normal donors. These results support the hypothesis that macroglobulinemia in TSS results from defective immunoregulatory control of B cell function, and that this may be caused by lysis of suppressor T cells by specific lymphocytotoxic antibodies produced by patients with this syndrome.

The immunology of malaria--a view from the bush

During the past few years a great deal has been learnt about malaria parasites and the immune responses that they evoke in their hosts. However, this new knowledge has so far had little impact on the practical problems of malaria control in tropical developing countries where malaria is still responsible for much mortality and morbidity. In Africa the malaria situation is now more serious than it was 20 years ago. Exciting new developments in molecular biology suggest that this situation may change in a few years time but attempts should be made to put the advances that have been made to the best practical use as soon as possible rather than delaying until even better technologies have been developed. This approach will require close collaboration between immunologists in sophisticated laboratories in industrialised countries and smaller laboratories in the countries of the developing world where malaria is still a major problem.

Cellular immune findings in Lyme disease. Correlation with serum IgM and disease activity

Cellular immune findings were studied in 48 patients with various stages of Lyme disease. At each stage, some patients, particularly those with neuritis or carditis, had elevated serum IgM levels and lymphopenia. During early disease, mononuclear cells tended to respond normally to phytohemagglutinin, and spontaneous suppressor cell activity was greater than normal. Later, during active neuritis, carditis, or arthritis, the trend was toward heightened phytohemagglutinin responsiveness and less suppression than normal. By multiple regression analysis, serum IgM levels correlated directly with disease activity (p = 0.025) and inversely with the number of T cells (p = 0.02); during acute disease only, elevated IgM levels correlated with increased phytohemagglutinin responsiveness (p = 0.004) and decreased suppressor cell activity (p = 0.03). Decreased suppression, observed later in the disease, may permit damage to host tissues because of either autoimmune phenomena or a heightened response to the Lyme spirochete.

Reduction of suppressor T lymphocytes in the tropical splenomegaly syndrome

To study the pathogenesis of tropical splenomegaly syndrome, we compared immunologic findings in patients from Flores, Indonesia, with those obtained in local residents without splenomegaly and in controls. Villagers with tropical splenomegaly syndrome had markedly elevated levels of total IgM, higher titers of IgM antibodies to Plasmodium vivax, and reduced levels of circulating T lymphocytes. The latter were caused by a decrease in the total number of T cells with the suppressor/cytotoxic phenotype (T8+). Levels of B lymphocytes were similar in all groups. All immunologic abnormalities reverted toward normal in patients treated weekly for 9 to 26 months with chloroquine phosphate. These findings suggest that overproduction of immunoglobulins in patients with tropical splenomegaly syndrome is caused by an imbalance in the normal ratio of helper: suppressor T cells that regulate B-lymphocyte function, and that this imbalance is due to a decrease in suppressor T lymphocytes.

Massive splenomegaly in Northern Zambia. I. Analysis of 344 cases

Massive splenomegaly is common in Northern Zambia. Nearly 40% of 344 patients were diagnosed as Tropical Splenomegaly Syndrome of malarial origin. Portal hypertension, lymphoreticular and haemopoietic malignancies, and schistosomiasis accounted for another 46%. The common causes of splenomegaly show differences of frequency within Zambia and also between Zambia and other African countries.