The existence of immunity to Onchocerca volvulus (Ov) infection is suggested by the presence of uninfected persons in hyperendemic areas. A major barrier to the study of immunity has been the correct identification of putatively immune (PI) subjects. To identify a PI group in a hyperendemic area in Ecuador, clinical and epidemiologic information was combined with a polymerase chain reaction (PCR)-based assay identifying Ov DNA in skin snips and a recombinant antigen-based ELISA. Comparison of immune responses revealed that PI subjects had significantly lower levels of Ov-specific IgG, IgG subclasses, and IgE than infected (INF) subjects. Female subjects were significantly more likely to be PI than male subjects, and INF female subjects had significantly lower levels of Ov-specific IgG, IgG1, and IgG3 than INF male subjects. Thus, the use of molecular-based techniques has helped to define more precisely the PI state in onchocerciasis.

Persons putatively immune (PI) to Onchocerca volvulus (Ov) infection were identified in Ecuador on the basis of epidemiologic, clinical, and parasitologic findings. Immune responses of PI subjects to a recombinant onchocercal protein, OvMBP20/11, were determined and compared with those of a comparable infected (INF) group from the same Ov-endemic area. PI subjects had significantly less antibody reactivity to this molecule; however, not all INF subjects had an antibody response. IgG1 and IgG4 were the predominant IgG subclasses induced to this molecule, and the amount of IgG1 produced was the only significant difference between the PI and INF groups. In contrast to the antibody responses, proliferative responses to OvMBP20/11 were significantly higher in PI than in INF subjects. Cytokine analysis of peripheral blood mononuclear cell culture supernatants revealed that INF subjects produced significantly more interleukin-10 in response to OvMBP20/11 than did PI subjects. This antigen induced few other cytokines, and there were no differences between study groups.

Afro-Ecuadorian individuals from an area where Onchocerca volvulus is hyperendemic have been monitored for infection over the past 16 years. To determine whether in utero exposure to O. volvulus biases a child's subsequent immune responses, children (9 to 16 years old) for whom the mother's infection status was known were chosen for study. Children of infected mothers (n ‫؍‬ 19) had significantly higher levels of skin microfilariae than children of uninfected mothers (n ‫؍‬ 13; P ‫؍‬ 0.021). While the serum levels of O. volvulus-specific immunoglobulin G (IgG), IgG subclasses, and IgE showed no significant differences between the two groups of children, peripheral blood mononuclear cells of children of infected mothers produced higher levels of Th2-type cytokines to several parasite antigens and lower levels of Th1-type cytokines to nonparasite antigens than those of children of uninfected mothers. Thus, in utero exposure to O. volvulus has a long-term effect on the child's subsequent cellular immune response that may render the child more susceptible to O. volvulus infection postnatally.

Isotype/subclass-specific antibody responses to adult Onchocerca volvulus extract (OvAg) were assessed by both ELISA and immunoblotting for a group of putatively immune individuals (PIs, n = 29) from a hyperendemic area in Ecuador and for a group of infected individuals (INFs, n = 470) from the same regions. As a group, the PIs have been previously shown to possess lower levels of OvAg specific IgG1, IgG2, IgG3 and IgG4 than INF's but semi-quantitative analysis revealed that the relative proportions of these subclasses differs between the two groups. The IgG of the PI group contained a higher proportion of IgG3 and a lower proportion of IgG4 than the INF group. The frequency distribution of IgG3 responses was similar for the PI and INF groups. The frequency distributions for IgG1, IgG4 and IgE were significantly different between the PI and INF groups. A subgroup of the PIs were identified from frequency distributions and multivariate plots of individual isotype responses as having antibody responses (mainly IgG4) possibly indicative of cryptic infection. High IgE responses were exclusive to INF individuals, and a rare response type of high IgG3 with negligible levels of other isotypes/subclasses was seen only in the PI group. However, the majority of the PIs had negligible responses for all antibody classes. Immunoblots demonstrated no obvious differences in qualitative recognition between the PIs and INFs.

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An ELISA test was developed to detect Paragonimus-specific antibodies, including IgG subclasses, using P. mexicanus crude water-soluble antigens. The test was standardized to detect antibodies in sera of Ecuadorian patients with pulmonary paragonimiasis and negative controls from the endemic area. The detected mean levels of IgG (0.753, SEM: 0.074) and IgM (0.303, SEM: 0.033) were significantly elevated (P < 0.05). Within the IgG subclasses, IgG4 showed the highest detected mean level (0.365, SEM: 0.116) and the other three subclasses showed considerably lower mean levels (IgG1, 0.186 SEM: 0.06; IgG2, 0.046 SEM: 0.01; IgG3, 0.123 SEM: 0.047). The number of P. mexicanus eggs found in sputum of infected individuals showed a positive correlation with the level of antibodies detected for IgM, IgG and its subclasses (P < 0.001). The relevance of these findings in Ecuadorian patients suffering from pulmonary paragonimiasis is discussed.