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Plasmodium-specific atypical memory B cells are short-lived activated B cells

ABSTRACT: Chronic infections such as HIV, tuberculosis and malaria in humans are associated with the appearance of atypical memory B cells in peripheral blood. It has been suggested that these B cells do not function normally as memory cells, and thus may be responsible for poor acquisition of immunity and maintenance of chronic infections. Studies on these cells in human infections are limited by the lack of accessibility to lymphoid organs, and relevant mouse models would be valuable to investigate their development, functional capacities, and role. To investigate Plasmodium-specific memory B-cell responses during malaria, we generated an immunoglobin heavy chain knock-in mouse with a B-cell receptor that recognizes the merozoite surface protein (MSP)-1 of the rodent malaria parasite, Plasmodium chabaudi. Using this mouse and a P. chabaudi infection initiated by infected mosquito bites we show that antigen-specific B cells with many characteristics of human atypical memory B cells are generated. These cells are immunoglobulin class-switched and express, among others, the cell surface molecules CD11c, CD11b, FCRL5, and some inhibitory receptors including PD1 and LAIR-1, as well as the transcription factor T-bet. Antigen-specific atypical memory B cells are detected side-by-side with classical memory B cells during chronic blood-stage infection. Whereas classical memory B cells persist after complete infection clearance, atypical memory B cells are short-lived and disappear from the spleen at the resolution of chronic infection. Short-lived Plasmodium-specific atypical B cells also appear transiently after immunization with a TLR7/8 ligand and MSP-1. Our data suggest that these atypical memory B cells are not a subset of memory B cells, but rather antigen-experienced activated cells, and part of a normal ongoing response. Their persistence over weeks in malaria and other infections may be a consequence of continued and chronic antigenic stimulation.

ORGANISM(S): Mus musculus

PROVIDER: GSE115155 | GEO | 2018/11/01

REPOSITORIES: GEO

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Project description:Plasmodium multigene families are thought to play important roles in the pathogenesis of malaria. Plasmodium interspersed repeat (pir) genes comprise the largest multigene family in many Plasmodium species. However, their expression pattern and localisation remain to be elucidated. Protein subcellular localisation is fundamental to be able to elucidate the functional importance and cell-cell interactions of the PIR proteins. Here, we use the rodent malaria parasite, Plasmodium chabaudi chabaudi, as a model to investigate the localisation pattern of this gene family. We found that most PIR proteins are co-expressed in clusters during acute and chronic infection; members of the S7 clade are predominantly expressed during the acute-phase, whereas members of the L1 clade dominate the chronic-phase of infection. Using peptide antisera specific for S7 or L1 PIRS, we show that S7 and L1 PIRs have different localisations within the infected red blood cells. S7 PIRs are exported into the infected red blood cells cytoplasm where they are co-localised with parasite-induced host cell modifications termed Maurer's clefts, whereas L1 PIRs are localised on or close to the parasitophorous vacuolar membrane. This localisation pattern changes following mosquito transmission and during progression from acute- to chronic-phase of infection. However, neither S7 nor L1 PIR proteins detected by the peptide antisera are localised on the surface of infected red blood cells, suggesting that they are unlikely to be targets of surface variant-specific antibodies or be involved directly in adhesion of infected red blood cells to host cells, as described for Plasmodium falciparum VAR proteins. Their presence on Maurer’s clefts, as seen for Plasmodium falciparum RIFIN and STEVOR proteins, might further suggest trafficking of the PIRs on the surface of the infected erythrocytes. The differences in subcellular localisation of the two major clades of Plasmodium chabaudi PIRs across the blood cycle, and the apparent lack of expression on the red cell surface strongly suggest that the function(s) of this gene family may differ from those of other multigene families of Plasmodium, such as the var genes of Plasmodium falciparum.

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Plasmodium-specific atypical memory B cells are short-lived activated B cells

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