Figure 2.

IgG4 extracted from a patient with cancer reacted to cancer-bound IgG1 and blocked antibody-mediated cancer immunity. (A) Upper panel: These photos serve as an example of the reactivity of IgG1 and IgG4 extracted from patients with cancer. IgG1 from the serum of a patient with breast cancer was labeled with biotin and stained a frozen cancer tissue section of the same patient. Cancer cells were positively stained by IgG1 (left). The cancer cells were confirmed by their characteristic histopathology of H&E staining (middle). IgG4 from serum of the same patient labeled with biotin and applied on the same cancer on a consecutive section was completely negative (right). Lower panel: Another breast cancer positively stained by IgG1 from the patient’s serum (left). The cancer cells were identified by positive immunostaining of cytokeratin (CK) on a consecutive section (middle). IgG4 from the same patient was not reactive to the same cancer on a consecutive section (right). (B) The upper panel illustrates the principle of the experimental reactions, and the middle and lower panels show staining results from two patients with breast cancer. Left: IgG1 from a patient with cancer positively reacted to frozen cancer tissue of the same patient (brown cells). Middle: IgG4 from the same patient with cancer applied to consecutive sections, but did not react to the same cancer. Right: However, when unlabeled IgG1 was applied to the same cancer tissue section followed by biotin-labeled IgG4, the cancer cells were positively stained (brown cells).