title: Changes in B Cell Populations and Merozoite Surface Protein-1-Specific Memory B Cell Responses after Prolonged Absence of Detectable P. falciparum Infection.
abstract: Clinical immunity to malaria declines in the absence of repeated parasite exposure. However, little is known about how B cell populations and antigen-specific memory B cells change in the absence of P. falciparum infection. A successful indoor residual insecticide spraying campaign in a highland area of western Kenya, led to an absence of blood-stage P. falciparum infection between March 2007 and April 2008. We assessed memory B cell responses in 45 adults at the beginning (April 2008) and end (April 2009) of a subsequent 12-month period during which none of the adults had evidence of asymptomatic parasitemia or clinical disease. Antibodies and memory B cells to the 42-kDa portion of the merozoite surface protein-1 (MSP-142) were measured using ELISA and ELISPOT assays, respectively. B cell populations were characterized by flow cytometry. From 2008 to 2009, the prevalence of MSP-142-specific memory B cells (45% vs. 55%, respectively, P = 0.32) or antibodies (91% vs. 82%, respectively, P = 0.32) did not differ significantly, although specific individuals did change from positive to negative and vice versa, particularly for memory B cells, suggesting possible low-level undetected parasitemia may have occurred in some individuals. The magnitude of MSP-142-specific memory B cells and levels of antibodies to MSP-142 also did not differ from 2008 to 2009 (P>0.10 for both). However, from 2008 to 2009 the proportions of both class-switched atypical (CD19+IgD-CD27-CD21-IgM-) and class-switched activated (CD19+IgD-CD27+CD21-IgM-) memory B cells decreased (both P<0.001). In contrast, class-switched resting classical memory B cells (CD19+IgD-CD27+CD21+IgM-) increased (P<0.001). In this area of seasonal malaria transmission, a one- year absence of detectable P. falciparum infection was not associated with changes in the prevalence or level of MSP-142 specific memory B cells, but was associated with major changes in overall memory B cell subsets.
authors.affiliation: Maseno University, Maseno, Kenya.
authors.forename: Cyrus
authors.initials: C
authors.lastname: Ayieko
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Maue
authors.forename: Walter G Z O
authors.initials: WG
authors.lastname: Jura
authors.forename: Gregory S
authors.initials: GS
authors.lastname: Noland
authors.forename: George
authors.initials: G
authors.lastname: Ayodo
authors.forename: Rosemary
authors.initials: R
authors.lastname: Rochford
authors.forename: Chandy C
authors.initials: CC
authors.lastname: John
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000906:Antibodies / Q000097:blood; D000907:Antibodies, Bacterial / Q000097:blood; D001402:B-Lymphocytes / Q000276:immunology*; D005260:Female; D006801:Humans; D007156:Immunologic Memory; D007630:Kenya; D016778:Malaria, Falciparum / Q000453:epidemiology / Q000276:immunology*; D008297:Male; D020066:Merozoite Surface Protein 1 / Q000276:immunology*; D008875:Middle Aged; D010641:Phenotype; D010963:Plasmodium falciparum; D015995:Prevalence; D011446:Prospective Studies; D013745:Tetanus Toxoid / Q000276:immunology; D055815:Young Adult
chemical_list: D000906:Antibodies; D000907:Antibodies, Bacterial; D020066:Merozoite Surface Protein 1; D013745:Tetanus Toxoid