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. 2017 Jan 10:5:e2855.
doi: 10.7717/peerj.2855. eCollection 2017.

Interferon- γ responses to Plasmodium falciparum vaccine candidate antigens decrease in the absence of malaria transmission

Cyrus Ayieko #  1 , Bilha S Ogola #  2 , Lyticia Ochola  3 , Gideon A M Ngwena  4 , George Ayodo  5 , James S Hodges  6 , Gregory S Noland  7 , Chandy C John  8
Affiliations

Interferon- γ responses to Plasmodium falciparum vaccine candidate antigens decrease in the absence of malaria transmission

Cyrus Ayieko et al. PeerJ. .

Abstract

Background: Malaria elimination campaigns are planned or active in many countries. The effects of malaria elimination on immune responses such as antigen-specific IFN- γ responses are not well characterized.

Methods: IFN- γ responses to the P. falciparum antigens circumsporozoite protein, liver stage antigen-1, thrombospondin-related adhesive protein, apical membrane antigen-1, MB2, and merozoite surface protein-1 were tested by ELISA in 243 individuals in highland Kenya in April 2008, October 2008, and April 2009, after a one-year period of interrupted malaria transmission from April 2007 to March 2008.

Results: While one individual (0.4%) tested positive for P. falciparum by PCR inOctober 2008 and another two (0.9%) tested positive in April 2009, no clinical malaria cases were detected during weekly visits. Levels of IFN-γ to all antigens decreased significantly from April 2008 to April 2009 (all P < 0.001).

Discussion: Naturally acquired IFN- γ responses to P. falciparum antigensare short-lived in the absence of repeated P. falciparum infection. Even short periods of malaria interruption may significantly decrease IFN-γ responses to P. falciparum antigens.

Keywords: Highland Kenya; Interferon gamma; Malaria; Plasmodium falciparum.

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Conflict of interest statement

The authors declare there are no competing interest

Figures

Figure 1
Figure 1. Proportion of individuals with positive IFN-γ responses to P. falciparum antigens in April 2008, October 2008 and April 2009.
The prevalence of antigen-specific responses across time was assessed by the chi-square test for trend. The P values are indicated across the bars. Bars marked with double asterisks (**) differ significantly (P < 0.05) from baseline (April 2008).
Figure 2
Figure 2. IFN-γ levels in response to P. falciparum antigens at baseline (April 2008), October 2008, and April 2009.
For each antigen, only individuals with a positive response in at least one time point were included in the analysis. The respective N values for the antigens were 144, 165, 169, 142, 194 and 183, respectively, for CSP, LSA, TRAP, AMA, MB-2 and MSP-1. The median IFN-γ level at each time is indicated by a square, 90th percentile by a circle, and 75th percentile by a triangle. Non-responders are placed below responders by giving them an artificial level of 0.01 and then “jittering” their levels (adding random noise) vertically to give an accurate sense of the number of non-responders.
Figure 3
Figure 3. Proportion of individuals with positive IFN-γ responses to the P. falciparumantigens CSP, LSA-1, MB2, TRAP, AMA-1, MB2 and MSP-1 across ages in April 2008 (A), October 2008 (B) and April 2009 (C).
IFN-γ responses across age-groups were compared by Fischer’s exact test. The P values for each antigen are indicated.
See this image and copyright information in PMC

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