Intestinal antilectin immunoglobulin A antibody response and immunity to Entamoeba dispar infection following cure of amebic liver abscess

Abstract

We followed 93 subjects with amebic liver abscess (ALA) and 963 close associate controls at 3-month intervals for 36 months to characterize intestinal and humoral antibody responses to the amebic galactose-inhibitable lectin and to determine whether immunity developed to Entamoeba histolytica or Entamoeba dispar infection following cure of ALA. We found that ALA subjects had a higher prevalence and level of intestinal antilectin immunoglobulin A (IgA) and serum anti-LC3 (cysteine-rich recombinant lectin protein) IgA and IgG antibodies, P < 0.01 and P < 0.05, respectively, compared to controls. The intestinal antilectin IgA antibody response was sustained over a longer time period in ALA subjects (71.8% remained positive at 18 months and 52.6% at 36 months, P < 0.001 compared to 17.6% and 10.3% of controls, respectively). ALA subjects were highly immune to E. dispar infection throughout the study (0% infected at 6 and 36 months, compared to 6.5% and 4.9% of control subjects, respectively, P < 0.05). Upon entry into the study, 6.3% of ALA subjects were infected with E. histolytica; the incidence of new E. histolytica infections in controls (as determined by culture) was too low (1.4%) to determine whether ALA subjects exhibited immunity to new infections. We found that stool cultures every 3 months markedly underestimated the occurrence of new E. histolytica infections, as 15.3% of controls seroconverted after 12 months of follow-up. Unfortunately, under the field conditions present in Durban, South Africa, enzyme-linked immunosorbent assay for detection of lectin antigen in stool yielded unreliable results. In summary, subjects cured of ALA exhibited sustained mucosal IgA antibody responses to the amebic galactose-inhibitable lectin and a high level of immunity to E. dispar infection. Determination of immunity to E. histolytica following cure of ALA will require the use of more sensitive and reliable diagnostic methods.

FIG. 1.

Prevalence of a positive ELISA for intestinal antilectin IgA antibodies in subjects cured of ALA (light bars) and controls (dark bars). The prevalence of antilectin IgA antibodies was greater in cases than controls at baseline (0 to 6 months) and during each follow-up period (P < 0.0001, for each). There was a significant decrease in the prevalence of antilectin IgA antibodies between baseline and follow-up intervals in ALA cases (P < 0.01 for each comparison) and in close associate controls (0 to 6 and 9 to 18 months compared to 21 to 36 months, P < 0.05).

FIG. 2.

Prevalence of serum anti-LC3 IgA (A) and IgG antibodies (B) for subjects cured of ALA (light bars) and controls (dark bars). The prevalence of a positive test for each antibody studied was greater in ALA subjects than controls at baseline and during each follow-up period (P < 0.001 for each). The prevalence of serum anti-LC3 IgA antibodies increased in controls only at 9 to 18 months (P < 0.001); in ALA cases there was a decrease in the prevalence of anti-LC3 IgG antibodies during each follow-up period (P < 0.001 compared to the previous period.

FIG. 3.

Percentage of ALA (light bars) and controls (dark bars) individuals ever having a positive test over the entire 36 months of the study. ALA subjects had a higher cumulative positive percentage for each antibody studied compared to controls, P < 0.01. Of interest, the cumulative percentage of control subjects with fecal antilectin IgA antibodies was greater than for either serum anti-LC3 IgA or IgG antibodies (P < 0.005).

FIG. 4.

Comparison of ELISA OD values at baseline (0 to 6 months) between antibody-positive ALA subjects and controls for intestinal antilectin IgA and serum anti-LC3 IgA antibodies. Fecal antilectin IgA antibody (dashed line) OD values are higher at each percentile (except 100%) for ALA cases (▴) compared to antibody-positive controls (▪) (P = 0.001 for each). The same was true for serum anti-LC3 IgA antibodies (solid line), P < 0.001 comparing ALA cases (▴) to controls (▪).