The protective role of antibodies to blood stage infections was demonstrated through passive transfer studies ( 3). These findings contribute to the understanding of acquisition and maintenance of immune responses to malaria.Īcquisition of clinical immunity to malaria is achieved after multiple infections in individuals living in areas with high transmission ( 1, 2). We conclude that the multiplexed B-cell FluoroSpot is a powerful tool for assessing antigen-specific MBC responses to several antigens simultaneously, and that the kinetics of MBC responses against merozoite surface antigens differ over the course of one year. We further found that individuals experiencing a primary infection could mount and maintain parasite-specific MBCs to a similar extent as previously exposed adults, already after a single infection. We show that the FluoroSpot assay can detect MBCs to all four merozoite antigens in the same well, and that the breadth and kinetics varied between individuals. We used the assay to study the kinetics of the MBC response after an acute episode of malaria and up to one year following treatment in travelers returning to Sweden from sub-Saharan Africa. Here, we developed a multiplexed reversed B-cell FluoroSpot assay capable of simultaneously detecting MBCs specific for the four Plasmodium falciparum blood-stage antigens, MSP-1 19, MSP-2, MSP-3 and AMA-1. However, frequencies of antigen-specific MBCs are low in peripheral blood, limiting the number of antigens that can be studied, especially when small blood volumes are available. Memory B cells (MBCs) are believed to be important for the maintenance of immunity to malaria, and these cells need to be explored in the context of different parasite antigens and their breadth and kinetics after natural infections. 7Department of Molecular Biosciences, The Wenner-Gren Institute, Stockholm University, Stockholm, Sweden.6Kenya Medical Research Institute (KEMRI)/Wellcome Trust Research Programme, Kilifi, Kenya.5Department of Clinical Microbiology, Karolinska University Hospital, Stockholm, Sweden.4Division of Biostatistics, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.3Department of Infectious Diseases, Karolinska University Hospital, Stockholm, Sweden.1Division of Infectious Diseases, Department of Medicine Solna, Karolinska Institutet and Center for Molecular Medicine, Stockholm, Sweden.Peter Jahnmatz 1,2*, Christopher Sundling 1,3, Victor Yman 1, Linnea Widman 4, Muhammad Asghar 1,3, Klara Sondén 1,3, Christine Stenström 5, Christian Smedman 2, Francis Ndungu 1,6, Niklas Ahlborg 2,7 and Anna Färnert 1,3*