Babesia divergensandPlasmodium falciparumUse Common Receptors, Glycophorins A and B, To Invade the Human Red Blood Cell

Abstract

Babesiosis has long been recognized as an economically important disease of cattle, but only in the last 30 years has Babesia been recognized as an important pathogen in humans. Invasion of erythrocytes is an integral part of the Babesia life cycle. However, very little information is available on the molecules involved in this process, in contrast to another hemoparasite, Plasmodium falciparum. Using invasion assays into normal red blood cells (RBCs), enzyme-treated cells, and clinically mutant cells, we showed that Babesia divergens uses neuraminidase-and trypsin-sensitive receptors to enter the RBCs, of which glycophorins A and B are the prominent ones. These results could have broad implications relating to evolutionarily conserved mechanisms of host cell entry in these related Apicomplexan parasites and pave the way toward a detailed molecular analysis of erythrocyte invasion in B. divergens.Babesiosis, caused by infection with intraerythrocytic parasites of the genus Babesia, is one of the most common infections of free-living animals worldwide and is gaining increasing interest as an emerging zoonosis, a disease that is communicable from animals to humans (17,26). The rodent parasite Babesia microti and the bovine pathogen Babesia divergens are responsible for most of the ϳ500 human infections that have been reported so far (26). Parasites that live in red blood cells (RBCs) have rather ingenious ways of gaining entry into these cells, thus escaping the dangers of the host immune system. Although there are many erythrocyte-seeking protozoa, most data regarding erythrocyte invasion have come from studies on Plasmodium, a related Apicomplexan parasite. In both parasites, invasion has been shown to be composed of an initial phase of random cell-cell contact, subsequent reorientation, and specific receptor-ligand interactions (6,14,15,25). However, in contrast to Plasmodium falciparum, little is known about the molecules used by Babesia to attach and invade erythrocytes, and yet this is one of the most critical factors in the life cycle of the parasite.The Babesia blood stage merozoite is designed for one major role: to locate, bind to, and invade host RBCs. This is a very specific interaction; Babesia does not invade other host cells (15,26). This specificity implies the presence of a receptor(s) on the erythrocyte, which is recognized by a complementary ligand(s) on the parasite. Several Babesia molecules have been shown to bind RBCs in vitro and may thus play a role in invasion. In Babesia bovis, a merozoite surface antigen (MSA-2) (21) and a rhoptry-associated antigen (RAP-1) (22) have been shown to bind erythrocytes. In Babesia equi, two other merozoite antigens, EMA-1 and EMA-2, have also been shown to interact with the RBC membrane skeleton (18). The cognate RBC receptors for these molecules remain unknown, as has the identity of any erythrocytic receptor used by the invading Babesia merozoite.The work presented in this report is based on the hypothesis that erythrocyte invasion by B. divergens and P. ...

Babesia divergens Apical Membrane Antigen 1 and Its Interaction with the Human Red Blood Cell

“…The identity of the RBC receptor remains to be shown; however, due to the neuraminidase resistance of the binding profile, the sialic acid residues on the major sialo-glycoproteins molecules on the red cell, namely, the glycophorins A, B and C, can be ruled out as the cognate receptor for BdAMA1. Earlier, we had shown that glycophorins A and B function as invasion receptors (22) for the B. divergens merozoite, but clearly the sialic acid moieties on them are not involved in the interaction of BdAMA1 with the RBC.…”

“…Briefly, 0.2 ml of packed RBCs was treated with either 2 ml of a 1 mg/ml concentration of trypsin (treated with tosylsulfonyl phenylalanyl chloromethyl ketone; Sigma), 1 ml of a 1 mg/ml concentration of chymotrypsin (Sigma), or 0.1 ml of a 0.1 IU/ml concentration of neuraminidase (Sigma) for 30 min at 37°C. Cells treated with trypsin were then washed and treated with 0.5 mg/ml soybean trypsin inhibitor (Sigma) for 15 min at room temperature, as described earlier (22). The efficacy of each enzyme treatment was assessed in the Laboratory of Immunohematology, New York Blood Center, by assaying for the loss of RBC agglutinability using a panel of monoclonal antibodies against suitable antigenic determinants on different blood group proteins.…”

“…Erythrocytes collected in 10% citrate-phosphate-dextrose were washed three times in PBS and treated with the various enzymes as described previously (22). Briefly, 0.2 ml of packed RBCs was treated with either 2 ml of a 1 mg/ml concentration of trypsin (treated with tosylsulfonyl phenylalanyl chloromethyl ketone; Sigma), 1 ml of a 1 mg/ml concentration of chymotrypsin (Sigma), or 0.1 ml of a 0.1 IU/ml concentration of neuraminidase (Sigma) for 30 min at 37°C.…”

Detection and quantification of Duffy antigen on bovine red blood cell membranes using a polyclonal antibody

“…Little is known about the molecular interactions between Babesia parasites and their receptors on the bovine host cell surface (Lobo 2005). Cattle infected with B. bigemina and B. bovis present clinical signs very similar to those of human beings infected with Plasmodium vivax and Plasmodium falciparum (Cooke et al 2005).…”

“…The genera Babesia and Plasmodium belong to phylum Apicomplexa and present similar features such as invasion of host cells (Taylor et al 1990, Dubremetz 1998, Menard 2001, Cowman & Crabb 2006, which demands an interaction between a speciϐic receptor on the vertebrate red blood cell (RBC) membrane and a ligand on the parasite surface (Lobo 2005, Yokoyama 2006. Little is known about the molecular interactions between Babesia parasites and their receptors on the bovine host cell surface (Lobo 2005).…”