Immunoproteomics of Plasmodium falciparum-infected red blood cell membrane fractions

Abstract

BACKGROUNDThe surface of infected red blood cells (iRBCs) has been widely investigated because of the molecular complexity and pathogenesis mechanisms involved. Asymptomatic individuals are important in the field because they can perpetuate transmission as natural reservoirs and present a challenge for diagnosing malaria because of their low levels of circulating parasites. Recent studies of iRBC antibody recognition have shown that responses are quantitatively similar in symptomatic and asymptomatic infections, but no studies have characterised the plasmodial proteins targeted by this response.OBJECTIVESOur main objective was to identify Plasmodium falciparum proteins associated with iRBC ghosts recognised by antibodies in the sera of symptomatic and asymptomatic individuals in the Brazilian Amazon.METHODSWe collected symptomatic and asymptomatic sera from patients residing in the Brazilian Amazon and P. falciparum iRBC ghosts to identify the proteins involved in natural antibody recognition by 2D-electrophoresis, western blotting, and high- resolution mass spectrometry.FINDINGS2D gel-based immunoproteome analysis using symptomatic and asymptomatic sera identified 11 proteins with at least one unique peptide, such as chaperones HSP70-1 and HSP70-x, which likely are components of the secretion machinery/PTEX translocon. PfEMP1 is involved in antigenic variation in symptomatic infections and we found putative membrane proteins whose functions are unknown.MAIN FINDINGSOur results suggest a potential role of old and new proteins, such as antigenic variation proteins, iRBC remodelling, and membrane proteins, with no assigned functions related to the immune response against P. falciparum, providing insights into the pathogenesis, erythrocyte remodelling, and secretion machinery important for alternative diagnosis and/or malaria therapy.

Heat Shock Proteins as Immunomodulants

“…However, some Hsps are extruded to the cell surface particularly in response to physiological stress [ 3 , 4 ]. In addition, some Hsps of parasitic origin and antibodies that recognize them have been detected in the host circulatory system [ 4 , 5 , 6 ]. Thus, the Hsps of host and parasitic origin that end up in the host circulatory system ultimately interact with immune cells to modulate the function of the latter.…”

“…Plasmodium falciparum , the main agent of malaria expresses six Hsp70s, and antibodies that recognize two of these of these proteins: PfHsp70-1 and PfHsp70-x [ 92 , 93 ]; have been reported to be present in sera obtained from individual living in malaria endemic areas [ 6 ]. This suggests a possible role for these two proteins of parasitic origin in host immune modulation.…”

“…It is thought that Hsp70 bound onto the infected red blood cell membrane is thought to interact with GrB, leading to its uptake and subsequent selective lysis of the malaria parasite-infected red blood cells [ 100 ]. P. falciparum infected red blood cells harbor Hsp70 of human origin as well as the exported parasite protein, PfHsp70-x [ 6 , 93 ]. Thus, it is plausible that both human Hsp70 and PfHsp70-x may interact with natural killer cells to stimulate GrB release and leading to selective lysis of parasite infected red blood cells [ 16 ].…”

“…The presence of LPS contaminants in the recombinant proteins used in such assays confounds the data as LPS is a potent immune cell modulant ( Table 2 ). For example, it has been reported that people living in malaria endemic areas possess antibodies that recognize two malarial heat shock proteins, P. falciparum Hsp70-1 (PfHsp70-1) and PfHsp70-x suggesting that these two chaperones possess immunomodulatory properties [ 6 , 110 ]. On the other hand, a study by Pooe and colleagues [ 94 ], showed that recombinant PfHsp70-1 lacks immune modulatory activity when it was introduced to immune cells cultured in vitro.…”

Establishing Computational Approaches Towards Identifying Malarial Allosteric Modulators: A Case Study of Plasmodium falciparum Hsp70s

“…Effectively, PfHsp70-x and PfHsp70-1 are expressed during the critical asexual blood developmental stage of P. falciparum [23,24]. Moreover, both proteins are well recognized by antibodies in asymptomatic infections [25]. PfHsp70-1, localized in the nucleus and cytosol [20], is essential for parasitic survival [26].…”