Induction of malarial anaemia by haemozoin medicated suppression of erythropoiesis through dysregulation of IL-10 and IL-12 cytokines

Abstract

Severe malarial anaemia (SMA) is the leading cause of morbidity and mortality in young children less than five years residing in a Plasmodium falciparum holoendemic transmission area of western Kenya. Although the immunopathogenesis of SMA is largely uncharacterized, recent studies have shown that circulating interleukin-12 (IL12) production is suppressed during malarial anaemia. Since interleukin-10 (IL-10) and tumour necrosis factor alpha (TNF-a) suppress IL-12 production in a number of diseases, the profiles of these regulatory cytokines were investigated to determine the mechanism for IL-12 suppression in children with malarial anaemia. Moreover, monocytes and neutrophils acquire haemozoin (Hz) naturally during a malarial infection. In this study children aged three to thirty three months with Hz and healthy controls visiting the hospital were studied in a longitudinal prospective hospital-based design. Sample size was determined using sample size software. Malaria screening was performed using Giemsa-stained thick and thin blood films. Parasites were counted against 300 leucocytes and parasite density estimated using each individual's white blood cell (WBC) count. Hz was counted from 30 monocytes and 100 neutrophils and the level of haemozoination compared with haemoglobin levels, IL-10 and IL-12 production. Full haemogram was estimated using a Coulter counter. Multiplex assay was used to determine IL-10, IFN-y, TNF-a and IL-12p70 in plasma levels, which were then compared with Hz and haemoglobin (Hb) levels. Differences between median cytokine concentrations in various groups were tested using Kruskal Wallis test and pair wise comparisons using Mann-Whitney U test. The ratio of IL-l0:IL-12 was calculated for each individual and the difference among median ratio between various groups was compared using Mann-Whitney U test. Chi-square test was used to compare proportions. Results revealed that ingestion of naturally acquired malarial pigment (Hz) by monocytes increased the production of IL-10 and TNF-a, relative to IL-12, which correlated with increased severity of malarial anaemia. Further results revealed that elevated levels of Hz containing monocytes (HCM) (>10 %) was associated with significantly higher numbers of WBC (P < 0.0001), lymphocytes (P < 0.0001), and monocytes (P < 0.0001). In contrast, high HCM (> 10 %)'were inversely associated with red blood cells count (P < 0.0001), Hb (P < 0.0001), haematocrit (P < 0.0001), reticulocyte counts (P < 0.05), and platelet counts (P < 0.0001).It was concluded that elevated levels of Hz-deposition in monocytes are associated with increased severity of anaemia, leukocytic parameters and thrombocytopaenia.