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IgG subclasses are known to be differentially regulated by cytokines (elaborated by activated I cells), which act as growth factors and immunoglobulin switch factors on B cells. In leprosy, we have previously shown that IgG subclass antibodies to a purified recombinant antigen of Mycobacierium leprae (18 000 MW) are restricted to IgG1 and IgG3 across the disease spectrum. The only significant difference observed was that lepromatous patients with low to undetectable T-cell responses showed a strong correlation between IgG1 and IgG3 (P < 0.001) antibodies while tuberculoid patients who showed strong T-cell responses did not show such a correlation. To examine if these differences were related to T-cell-mediated class switching in tuberculoid leprosy patients, we have studied epitope recognition by IgG1 and IgG3 using a panel of synthetic peptides spanning the 18000MW molecule in an enzyme-linked immunosorbent assay (ELISA). In lepromatous patients there was little similarity in peptide recognition by IgG1 and IgG3, with IgG1 recognition being restricted to a single dominant carboxy-terminal peptide while the IgG3 antibodies recognized a diverse set of peptides in the N-terminal half of the 18 000 MW molecule. In tuberculoid patients both IgG1 and IgG3 antibody showed recognition of similar peptides in the N-terminal half of the 18 000 MW molecule. Our results therefore support the hypothesis that immunoglobulin class switching is occurring in tuberculoid but not in lepromatous patients. [ABSTRACT FROM AUTHOR]

IgG subclass responses to Mycobacterium leprae 18000MW recombinant antigen (18K) were determined in sera from untreated leprosy patients using an ELISA-based assay with specific monoclonal antibodies. Antibodies to M. leprae 18K were restricted to IgG1 and IgG3 antibodies with higher seropositivity in lepromatous patients (25.5% for IgG1 and 12.8% for IgG3) compared to patients with tuberculoid disease (11.5% for IgG1 and 5% for IgG3). No significant antibody response was detectable in IgG2 and IgG4 in patients with either lepromatous or tuberculoid leprosy. The selective production of antibodies in IgG1 and IgG3 subclasses could not be related to polyclonal activation in these subclasses as all IgG subclasses showed similar elevated levels at the polyclonal level. The major difference noted between lepromatous and tuberculoid leprosy patients with the IgG subclass antibody response was a strong linear correlation between IgG1 and IgG3 responses to M. leprae 18K in lepromatous patients (r = 0.703, P < 0.001) but not in tuberculoid leprosy patients (r = 0.007, P > 0.10) which may be related to immunoglobulin class switching of IgG3 to IgG1 rather than selective shifts in T-helper subsets. Our results therefore, do not support the hypothesis that activation of Th2 cells occurs in lepromatous leprosy; this issue needs further examination. [ABSTRACT FROM AUTHOR]

To explore the relative species specificities of the IgE and IgG antibody responses to helminth infections in man, we studied four pools of sera from patients infected with Wuchereria bancrofti, Brugia malayi, Onchocerca volvulus or Ascaris lumbricoides and ten individual sera from patients with onchocerciasis. IgE antibodies were detected by radioallergosorbent test (RAST) analysis and IgO antibodies by a Staphylococcus protein A radioimmunoassay (Staph A-RIA). Analysis of the binding curves with four different immunosorbents (prepared from antigens of B. malayi, O. volvulus, Dipesalonema viteae and A. lwnbricoides) in the RAST and the binding curves with these same four antigens in the Staph A-RIA confirmed the relative species specificities for both the IgE and IgO antibody responses. Then determination of these antibody levels after specific absorption of the sera with both homologous and heterologous antigens showed that in all instances there was significantly less cross-reactivity with heterologous parasite antigens (i.e. higher species specificity) in the IgE antibody. [ABSTRACT FROM AUTHOR]