Pro-inflammatory Cytokines Establish a Balance in Symptomatic and Asymptomatic Malaria in Plasmodium falciparum Endemic Regions

Background and Objectives: Pro-inflammatory cytokines are key in the control of malaria. This study profiled the pro-inflammatory cytokines: tumor necrosis factor-α (TNF-α), Interleukine–2 (IL-2), Interleukine–6 (IL-6) and Interleukine–12 (IL-12) in symptomatic and asymptomatic P. falciparum malaria in Abuja with the aim of elucidating their role in symptomatic and asymptomatic malaria.

Methodology: In the study, 246 plasma samples each from symptomatic and asymptomatic malaria volunteers were assayed for TNF-α, IL-2, IL-6 and IL-12 using Enzyme-Linked Immunosorbent Assay (ELISA) technique and values expressed in pictogram (pg).

Results: The study population comprised 48% male within which 50.4% were symptomatic and 49.6%) asymptomatic, 51.2% was female comprising 49.6% symptomatic and 50.4% asymptomatic. The median plasma concentration of TNF-α in symptomatic and asymptomatic groups of the population were 2.75pg and 2.04pg respectively and differed significantly (P<0.001), likewise IL-6: 4.83pg and 3.01pg (P = 0.014). IL-2 and IL-12 differed significantly in symptomatic and asymptomatic groups but the asymptomatic group showed higher levels of the cytokines: 3.20pg and 3.07pg (P<0.001) for IL-2, and 6.17pg and 3.40pg respectively (P<0.001) for IL-12. When segregated by study areas and age groups, TNF-α, IL-6 and IL-12 showed significant difference between the symptomatic and asymptomatic cases in age group 10-20years; but IL-2 showed no significant difference. TNF-α and IL-6 levels were higher in symptomatic than asymptomatic cases (2.80pg/2.05pg, P<0.001, and 5.2pg/2.42pg, P = 0.023 respectively), IL-12 was higher in asymptomatic case than symptomatic case (3.44pg/5.65pg, P<0.001). In age group 21-39years, TNF-α was significantly higher in symptomatic group than asymptomatic group (2.49pg/2.03pg, P< 0.001) however, IL-2 and IL-12 are significantly higher in asymptomatic than symptomatic cases (3.03pg/3.17pg, P<0.001 and 3.40pg/6.34pg, P < 0.001 respectively). In age group 40 years and above, only IL-2 and IL-12 showed significant difference with asymptomatic cases showing higher plasma levels of the cytokines (3.03pg/3.17pg, P<0.001, and 3.22pg/5.52pg, P<0.001) respectively.

Conclusion: The different patterns exhibited by the pro-inflammatory cytokines (TNF-α and IL-6 that were elevated in symptomatic cases, and IL-2 and IL-12 that were elevated in asymptomatic cases) show interplay among pro-inflammatory cytokines to regulate malaria manifestation in P. falciparum endemic place.