A Novel DBL-Domain of the P. falciparum 332 Molecule Possibly Involved in Erythrocyte Adhesion

Plasmodium falciparum malaria is brought about by the asexual stages of the parasite residing in human red blood cells (RBC). Contact between the erythrocyte surface and the merozoite is the first step for successful invasion and proliferation of the parasite. A number of different pathways utilised by the parasite to adhere and invade the host RBC have been characterized, but the complete biology of this process remains elusive. We here report the identification of an open reading frame (ORF) representing a hitherto unknown second exon of the Pf332 gene that encodes a cysteine-rich polypeptide with a high degree of similarity to the Duffy-binding-like (DBL) domain of the erythrocyte-binding-ligand (EBL) family. The sequence of this DBL-domain is conserved and expressed in all parasite clones/strains investigated. In addition, the expression level of Pf332 correlates with proliferation efficiency of the parasites in vitro. Antibodies raised against the DBL-domain are able to reduce the invasion efficiency of different parasite clones/strains. Analysis of the DBL-domain revealed its ability to bind to uninfected human RBC, and moreover demonstrated association with the iRBC surface. Thus, Pf332 is a molecule with a potential role to support merozoite invasion. Due to the high level of conservation in sequence, the novel DBL-domain of Pf332 is of possible importance for development of novel anti-malaria drugs and vaccines

Protozoal enteric infections among expatriates in Bangladesh

In order to study the prevalence, incidence, and symptoms of infections with Giardia lamblia and Entamoeba histolytica, we followed 251 expatriates in Bangladesh over a 1-year period. Microscopic examination of fecal specimens was performed upon enrollment, at 3-month intervals, and during episodes of diarrhea. Specimens were cultured for bacteria and samples of serum and saliva were collected for antibody studies (IgG and SIgA). The prevalence of G. lamblia infections was 5.2% and the incidence 11.8%. Children aged less than or equal to 10 years and newcomers were most frequently infected (P less than 0.02). Symptoms were present in 37% of the subjects infected with G. lamblia. A systemic antibody response was observed in 57% of symptomatic patients and 35% of asymptomatic subjects during the first 2 months of infection. The prevalence and the incidence of E. histolytica infection were 3.2% and 8.6%, respectively. Infections with E. histolytica were correlated with the duration of stay in Bangladesh; less than 1 year 7% vs. greater than 3 years 26% (P less than 0.01). Most expatriates infected with E. histolytica were asymptomatic (90%). Three adult patients, who were resident in Bangladesh for less than 1 year, were symptomatic but none of them developed dysentery or a serological response. Four of 25 asymptomatic subjects had significant antibody titers. Three of these people were seropositive for ameba at the beginning of the study. The local immune response, reflected by specific secretory IgA in saliva samples, correlated poorly with both E. histolytica and G. lamblia infection

Lymphocyte activation induced by Trichinella spiralis infection reflected as spontaneous DNA synthesis in vitro.

Spleen cells from mice, infected with Trichinella spiralis, were cultured in micro and macrocultures without stimulatory agents. As controls, various polyclonal T and B cell activators were used. During the course of the infection the cells exhibited an increased spontaneous DNA synthesis compared to the cells from uninfected controls. It was also found that the relative proportion of theta and Ig-positive cells and macrophages was not significantly affected by the infection. To characterize the in vivo stimulated cells one week after infection various techniques were used. Autoradiography combined with immunofluorescence revealed that virtually all labelled cells were Ig-negative. Removal of macrophages by silica powder decreased the spontaneous DNA synthesis but not to the level of the controls. Spleen cells from infected nude mice did not show any increased spontaneous DNA synthesis, whereas the effluent cells obtained after separation on Ig-complexed columns still showed an enhanced spontaneous DNA synthesis. These results indicate that T. spiralis infection causes a macrophage dependent activation of T cells which in vitro is detectable as spontaneous DNA synthesis

A comparative study of the immunohistological and serological response of intact and T cell-deprived mice to Trichinella spiralis.

Thymectomized, lethally irradiated CBA mice reconstituted with anti-theta-serum-treated bone-marrow cells (TxB) were infected with T. spiralis at the age of 11 weeks. Intact, age-matched T. spiralis infected and non-infected CBA mice served as controls. Sera were collected up to 26 days after infection and examined for the presence of total and class-specific antibodies by indirect immunoflourescence. Mesenteric lymph nodes, spleen and axillary lymph nodes were examined by conventional histopathology for the presence of pyroninophilic blast cells, plasma blasts and plasma cells. Immunoflourescence was applied to examine cells containing immunoglobulins of various classes. Antibodies against T. siralis were demonstrated both in intact and TxB mice from day 10 after infection onwards. The amount of antibodies was lower in the TxB than in the intact mice. This might indicate that besides thymus-dependent, also thymus-independent antibodies against Trichinella are formed. No difference was observed in the thymus-independent areas of the lymphoid tissues from both intact and TxB mice, with the exception of a lower increase in number of IgM-containing cells in T cell-deprived mice. A marked increase in pyroninophilic blast cells was found in the thymus-dependent areas of the intact mice after infection, whereas only a very limited increase was observed in the T cell-deprived mice. The data were interpreted as supporting the thymus dependency of host response against Trichinella