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Summary The biological activities of immunoglobulins are not affected equally by chemical modifications. The sites of IgG responsible for the fixation of complement and for the interaction with the rheumatoid factor seem to be more labile than those concerned with antibody activity. The destruction of Try and Met causes a drastic modification of the biological activities of both IgG and IgA, the latter being even somewhat more labile. The present study confirmed earlier results showing that there is not always a parallelism between the amount of aggregated material and anticomplementary activity in IgG. Certain chemically modified IgG preparations having lost their anticomplementary activity become again anticomplementary after heating and this activity can also be found after digestion with papain in certain modified Fc-fragments. However, other substituted IgG molecules are definitely devoid of anticomplementary activity.

Fraction III obtained during large acale fractionation of human plasma served as starting material for obtaining an immunoglobulin fraction enriched in IgA and IgM. Caprylic acid was used for the precipitation of most proteins other than the immunoglobulins present in fraction III. The proteins remaining in the supernatant are then precipitated vith ethanol at pH 6. Prealbumin is the main contaminant of this immunoglobulin preparation which contains 20–25% IgM and 15–20% IgA. The residual IgG can be removed by adsorption of the other proteins on DEAE-cellulose at pH 5.7 (0.03 M acetate), elution being achieved at pH 5.7 (0.2 M acetate).

A SPECIFIC serological activity was found several years ago in the serum of patients suffering from rheumatoid arthritis.

Compared with the tuberculin skin test, the antigen-specific interferon-gamma assays, using a combination of two antigens ESAT-6 and CFP-10, has higher specificity for the diagnosis of latent tuberculosis, better correlation with exposure to M. tuberculosis, no cross-reactivity due to BCG vaccination and less towards nontuberculous mycobacterial infection. Fewer false positive results in uninfected persons avoid the costs of unnecessary therapy and its possible side effects. In low endemic areas, interferon-y assays are useful in addition of diagnostic algorithm for individuals with suspected tuberculosis. Further studies are required to evaluate the utility of the interferon-gamma assays in specialised subgroups of patients (immunocompromised, young children, patients with extrapulmonary disease,...) and as a marker of disease activity.