Available studies trying to resolve the reason for the Fulani's relative protection against malaria have so far focused on immunological responses mostly in adults and not so much is known about these responses in children. The previously established relative protection for Fulani seen in adults was in this study shown to be evident during early childhood in this ethnic group. Children from the Fulani ethnic group had higher titres of malaria-specific antibodies and pro-inflammatory cytokine levels as well as unchanged chemokine levels upon an infection, as compared to Dogon children, suggesting that these differences are established already early in life.
Cytokines and chemokines are essential mediators during P. falciparum infection and the balance between pro- and anti-inflammatory cytokines may be important for the clinical outcome of malaria . Higher levels of all detectable cytokines were found in the Fulani group when comparing all Fulani children to all Dogon children, irrespective of infectious status. When children were further subdivided and the uninfected children from both ethnic groups were compared, the uninfected Fulani were found to have higher levels of IFN-α, IL-6, IL-8 and IL-12 compared to the uninfected Dogon. This indicates that Fulani children might be more prone to combat P. falciparum infections, possibly due to higher baseline levels of these cytokines.
When comparing the infected children from both ethnic groups, IFN-γ was the only factor out of all tested that was significantly increased in infected Fulani compared to infected Dogon. This observation is in line with previous findings by McCall and colleagues who reported that mononuclear cells from Fulani are able to produce a 10-fold stronger IFN-γ response after stimulation with Plasmodium parasites compared to cells from Dogon . Available studies in both humans and mice have demonstrated the importance of an early IFN-γ response as a crucial determinant in the outcome of the infection and the well-being of the patient [28, 29]. The result suggests that the increased levels of IFN-γ seen in infected Fulani may play a critical role in the difference in susceptibility to malaria in these two ethnic groups.
When comparing the uninfected children from both ethnic groups, the levels of IL-8 were found to be higher in uninfected Fulani compared to uninfected Dogon. However, when comparing differences within the same ethnic group, the levels of IL-8 were significantly lower in infected Fulani compared to their uninfected peers and this difference was not evident between infected and uninfected Dogon. IL-8 is a chemoattractant cytokine known to be involved in recruiting neutrophils to inflammatory sites. Very little information concerning the role for IL-8 in malaria pathogenesis/protection exists. IL-8 has been shown to be elevated in a small group of severe malaria cases in adults . In addition, high expression levels of IL-8 mRNA have also been demonstrated in placental malaria . Thus, the relevance for the lower levels of IL-8 that Fulani children exhibit upon infection is presently unknown and needs to be further investigated.
Further, the only cytokines that showed differences between infected and uninfected Dogon were IL-6 and IL-12p70. The results showed higher levels of IL-6 and IL-12p70 in infected Dogon compared to their uninfected counterparts, and these differences were not seen between infected and uninfected Fulani children. IL-6 is a major mediator of the acute phase response. Increased P. falciparum-induced IL-6 production has previously been associated with increased incidence of clinical episodes  and others have suggested IL-6 to be a marker for complicated P. falciparum malaria . The fact that IL-6 increased upon infection in Dogon but not in Fulani, might imply this cytokine to be important in the pathogenesis of malaria. IL-12p70 has a fundamental role in the induction of Th1-associated immunity. Low levels of IL-12p70 have been reported to be associated with severe malaria disease in children [34, 35]. The Fulani children had unchanged levels of IL-12p70 upon infection, while the levels increased in Dogon children. However, there were no correlations between the levels of IL-6 (p = 0.24, Rho = 0.28) and IL-12p70 (p = 0.26, Rho = -0.28) with parasitaemia, which could be due to small sample size in this study population.
The role of chemokines and their distribution in plasma has not been investigated in the Fulani and Dogon ethnic groups. The results from this study show that all chemokines tested were unchanged upon an infection in Fulani children, while this was not the case in Dogon. Infected Dogon children undergoing an infection had lower levels of RANTES compared to uninfected Dogon. Low levels of RANTES have previously been reported to be associated with mortality in children with severe malaria , in particular in cerebral malaria , and decreased levels have also been reported to be correlated with increased disease severity . One reason for the low levels of RANTES in severe malaria may be due to thrombocytopaenia that is often seen during these conditions, as platelets are a major reservoir of RANTES. The low level of RANTES seen in infected Dogon could thus be a result of destroyed platelets even though this was not tested.
The observed higher levels of MIG, MCP-1 and IP-10 in infected Dogon children compared to uninfected children. This marked up-regulation of chemokines was not evident in the infected Fulani children. Chemokines are involved in attracting different immune cell populations to the site of infections thereby aiding in the inflammatory response. Some of these factors have been implicated in severe malaria disease as well as in inflammatory diseases . High levels of IP-10 have been shown to be associated with increased risk of cerebral malaria associated mortality , IP-10 and MIG are required for development of murine cerebral malaria  and elevated levels of these factors have also been found in visceral leishmaniasis .
Taken together it seems Fulani already have high baseline levels of these chemokines in circulation compared to Dogon since the levels do not change when they become infected, again suggesting that they are more prepared for combating infections. Since chemokines such as MIG, MCP-1 and IP-10 are involved in cell migration, the lower frequencies of these chemokines found in uninfected Dogon might imply that these cells are not able to migrate as well as cells from uninfected Fulani. Interestingly, Arama and colleagues  reported that infected Dogon children have higher percentages of certain antigen-presenting cell (APC) subsets in circulation but that they are less activated compared to APC obtained from Fulani children. In contrast, the Fulani children had fewer but more activated APC in the circulation, which suggests that the cells have migrated to the secondary lymphoid organs and are therefore not seen in the circulation.
It has been known since the early 1960s that immunoglobulins (Ig) play an important role in malarial immunity . The result from this study indicates that the Fulani children have a stronger anti-malaria specific antibody response as compared to the Dogon, as revealed by higher titres of malaria-specific IgG and IgM antibodies. This has been reported earlier by others who compared adult Fulani with adults from their neighbouring ethnic groups, living in both Burkina Faso  and in Mali [14–16]. Previous studies have shown that antibody titres are correlated with age and parasitaemia , therefore the relationship between high parasitaemia and low antibody titres as well as a correlation between age and high antibody titres in these children was investigated. However, such analysis showed that there were no correlations for total IgG in infected Dogon (p = 0.63, Rho = 0.11) as well as for infected Fulani (p = 0.43, Rho = -0.32) between high parasitaemia and antibody titres. In contrast, the correlation between age and antibody titres showed an increase of total IgG antibodies with increasing age in uninfected Dogon (p = 0.005, Rho = 0.64), which was not the case in uninfected Fulani (p = 0.47, Rho = -0.17), suggesting that Fulani children already have high antibody titres irrespective of age in this study population. Similar results were found for IgG1 (p = 0.07, Rho = 0.40) and IgG3 (p = 0.02, Rho = 0.52) between age and antibody titres in the uninfected Dogon, which was not the case for uninfected Fulani (p = 0.57, Rho = -0.14) and (p = 0.23, Rho = 0.25) for IgG1 and IgG3, respectively.
To reassure that the malaria-specific antibodies are specific for the parasite, a control antigen of sonicated erythrocytes were included on all plates. There was no reactivity in any sera tested with sonicated erythrocytes confirming that the antibodies detected against the crude antigen are parasite specific.
Growing evidence supports that not all immunoglobulin subclasses are associated with protection against malaria, but rather it is the cytophilic subclasses; i.e. IgG1 and IgG3, that are important. IgG1 and IgG3 antibodies have shown to be crucial in parasite clearance by binding to the surface of the infected erythrocyte or to mediate opsonization by cooperating with human monocytes . The observed higher titres of malaria-specific antibodies in the Fulani compared to the Dogon for IgG1-IgG3 but not for IgG4 are in concordance with previous studies [14–16]. These differences were still significant when correcting for age (not listed). Regarding IgG3 levels, one interesting observation was made when dividing the children into infected and uninfected individuals. The infected Fulani had lower titres of IgG3 antibodies than uninfected children. This is surprising since IgG3 is an isotype that has previously been suggested to play an important role in the protection against malaria . One reason for the lower levels seen in Fulani could be that these antibodies have formed immune-complexes and thus are no longer detectable in the circulation. However, after correcting for age this difference was not statistically significant between the two groups anymore (not listed). The reason for this is not know but might be due to the different age distributions in the two groups (the infected Fulani children included the youngest children in the study) as well as the small sample size. Further studies are needed to clarify this.
The result showed that the titres of malaria-specific IgG2 and IgG4 antibodies were relatively low in both Fulani and Dogon. These antibodies are thought to inhibit the protective effects mediated by the cytophilic antibodies (IgG1 and IgG3) and could thereby potentially inhibit their neutralizing effect on the parasite. However, the role of IgG2 antibody has shown somewhat conflicting results and recent studies have indicated that this antibody may have a protective role against P. falciparum malaria in individuals carrying a certain Fcγ receptor subtype . Furthermore, it has also been shown that high levels of IgG2 in combination with low levels of IgG4 antibodies are associated with protection against malaria . There are also studies indicating that it is not the relative amount of these malaria-specific antibodies that is important, but rather the balance between the cytophilic and the non-cytophilic antibodies that determines the outcome during an infection .