Elevated levels of IgG3 and IgG4 subclass in paediatric cases of kala azar

Visceral leishmaniasis (VL) or Kala azar (KA) is a systemic disease caused by the parasites of the Leishmania donovani complex. Control measures rely on treatment with antileishmanial agents, however, fraught with problems such as toxicity or drug resistance. The incidence rate is on the rise for children, for reasons yet undefined. Previously we have shown significantly elevated level of IL-10 in children compared to adult KA cases. Here, antileishmanial antibody and C-reactive protein (CRP) levels were investigated in paediatrics and adult patients of KA and post-KA dermal leishmaniasis (PKDL). Level of IgG4 was significantly elevated in PKDL compared to KA, although total IgG and IgG1 were significantly lower. The antileishmania antibody levels of subclass IgG3 and IgG4 were found significantly elevated in paediatrics, however, levels of IgG, IgG1, IgG2 and CRP were comparable in paediatric and adult KA cases. In case of PKDL, levels of IgG and it subclass were similar in the two groups. No significant difference in antileishmanial antibody level was noticed between macular or polymorphic cases of PKDL. The differential antibody intensity in paediatric cases, together with significant level of circulating IL-10, could be considered as a marker of differential disease susceptibility.