Degradation of immunoglobulins by lysosomal enzymes of tumors-I. Demonstration of the phenomenon using mouse tumors

Lysosomal extracts derived from various mouse tumors degraded mouse immunoglobulins (Ig) upon in vitro incubation at pH 3·6 or at pH 3·8. The degradation was evaluated by a decreased ability of the treated Ig to form precipitates with corresponding monospecific antisera, by a modified gel filtration elution pattern revealing low mol. wt degratation products and by a decreased precipitability by ammonium sulfate and by cold TCA. The observation that the activity was pH and time dependent, was affected by the concentration of both the lysosomal extracts and the Ig and that the active factor in the lysosomal extract was heat labile, permitted the conclusion that lysosomal cathepsins were involved. There are some indications that mouse IgG1 and IgG2 may differ in their sensitivity to the lysosomal activity.