Plasmodium vivax: avaliação da resposta de anticorpos IgG em crianças expostas à malária

Abstract

An improved knowledge of human antiplasmodial defense mechanisms is partof current strategies against malaria. One of the effective defense mechanisms is the relationship between cytophilic antibodies and monocytes in order to increase the phagocytosis of infected cells. Comparative studies on immunoglobulin patterns have been carried out in immune and semi-immune populations.The present work is a further contribution to the subject and has the objectiveto study the response of IgG antibodies anti-P. vivax (IgG anti-PV), and their cytophilic (lgG1 e IgG3) and non-cytophilic (lgG2) subclasses in 34 outpatient children with malaria by P.vivax. Diagnosis of malaria was established by thick blood films. IgG levels, with their respective subclasses, were identified by indirect fluorescent antibody technique in the children enrolled in the study, during the acute phase and up to ultimate established cure. Patients were divided in 2 groups according to a previous malaria history (primarily infected, n= 28) and patients with history of previous malaria attack (n=6). The geometric means of antibodies IgG anti-PV levels were demonstrated during different periods of sera assessment. The IgG anti-PV levels obtained in the days zero and seven were compared (Student's t test). IgG anti-PV levels were correlated with assexual parasitaemia and the period of sickness, (Spearman's correlation test). A description of clinical features ocurred in both subgroups. Regarding immunoglobulin subclasses, the proportion of positive and negative sera was compared (Exact Fisher's test), in the 2 subgroups with the following results: a significative statistical difference (p=0,027) ocurred in the IgG levels between day zero (D0) and day seven (07), with no correlation with previous malaria history. A descending curve was observed in IgG levels, with mean and variable values respectively of 95,2% (40-2560) on the 60th day, 62,5% (40-320) on the 120th day, and 28% (40-160) on the 180th day after treatment. There was a positive association between the time of sickness and total antibody IgG anti-PV levels in primarily infected patients. The rank order for geometric means of IgG subclasses encountered was: IgG1(598,41) > IgG3 (4,06) > IgG2 (1,42). There were no significative differences in IgG anti-PV subclasses among primarily infected patients and those without previous malaria history. The following conclusions were made: 1) An increase of IgG anti-PV levels was seen between D0 and 07; 2) During the follow up the IgG anti-PV levels showing a gradual tendency to decline: 4,76% of the patients had negative results until 060, 37,5% until 0120, and 71,42% had negative results until 180 days after treatment; 3) There was no association between assexual parasitemia in day zero and antibody levels IgG anti-PV in the first and in the eighth day of treatment; 4) In children with previous malaria attacks the time of sickness evaluation is proporcional to antibody IgG anti-PV levels, and the reverse occurs, in the primarily infected children; 5) There was no correlation between total antibodies anti-PV levels and evidence of splenomegaly;6) Cytophilic antibodies (lgG1 > IgG3) predominated over noncytophilic antibodies (lgG2) in the study sample.