Aetiologic leads in the malignant lymphomas

The immunopathology of Hodgkin's disease

Answers are beginning to emerge to the questions posed in the introduction to the preceding section. In vitro techniques that allow characterization of malignant cells have particular relevance when, as in Hodgkin's disease, the precise identity of the cells remains in doubt. Monolayer tissue cultures derived from Hodgkin's disease tumours and maintained as established cell lines have proven amenable to a variety of cytogenetic, immunological, enzymatic, and ultrastructural studies. Tissue culture experiemnts, in conjunction with meticulous immunological studies of individual Reed-Sternberg cells from non-cultured tumours, suggest that neoplastic cells of Hodgkin's disease are related to, and possibly derived from, cells of the monocyte-macrophage system. The lymphocytes that comprise an integral part of the cellular proliferation and form the basis for histological subclassification of the tumour could be a manifestation of cell-mediated immunity against this non-lymphoid malignant cell. The immunodeficiency of patients with untreated Hodgkin's disease of limited anatomical extent is not the primary event of the disorder and probably not related to the site at which the aetiological agent acts. The deficit does not result solely from impaired T-cell function and appears to arise as a consequence of excessive suppressor cell activity. Inhibitory monocyte-lymphocyte interactions may be one of the causes of defective cell-mediated immunity in Hodgkin's disease. The possible significance of elevated levels of circulating immune complexes in the serum of patients with Hodgkin's disease is indicated by the finding that such complexes react with cells of long-term monolayer tissue cultures derived from the tumour. Circulating immune complexes may be one source for intracellular immunoglobulin in non-cultured Hodgkin's disease cells. The presence of polyclonal immunoglobulin G on the membrane and within the cytoplasm of Reed-Sternberg cells could be due to in vivo binding and ingestion of immune complexes by such cells. The specificity of the interaction between soluble complement-containing immune complexes and neoplastic cells of Hodgkin's disease depends on the nature of the complexed antigen. The complexes could non-specifically attach via an Fc receptor or, if the complexed antigen is identical to a tumour cell antigen, the binding could be specific. If the immune complexes are tumour specific they could provide a source for isolation and identification of tumour-associated antigens. However, the aetiological significance of antigens and putative oncogenic viruses thus far identified in association with Hodgkin's disease remains to be clarified.

Selectivity and rejectivity in cancer metastasis

In cancer metastasis, "selectivity" denotes the formation of secondary tumor in an organ in such a manner that its localization pattern is peculiar. The opposite phenomenon should be recognized and called "rejectivity". In man, carcinomas appear to spread selectively to the umbilicus, whereas lymphomas seem to reject that site. In all probability, recognition of the twin theory of selectivity and rejectivity will stimulate research on cancer dissemination.

Terminal deoxynucleotidyl transferase activity in malignant lymphomas

To determine the usefulness of terminal deoxynucleotidyl transferase enzyme activity as a biochemical marker in the study of lymphoma, we assayed 50 various malignant lymphomas as well as normal lymphoid tissue for this activity. Neoplastic cells from patients with Hodgkin's disease, Burkitt's tumor, Sézary's syndrome, chronic lymphocytic leukemia, leukemic reticuloendotheliosis and lymphocytic lymphomas (poorly differentiated and intermediate) were all without notable enzyme activity. Large-cell tumors of B-cell type were also negative. One of three large-cell tumors without B-cell or T-cell-surface specificity was positive (1.40 nmol per hour per milligram of DNA). Enzyme activity was consistently present only in lymphoblastic lymphomas (all six cases studied), with a mean activity of 7.80 nmol per hour per milligram of DNA. These six cases had heterogeneous surface immunomarkers. We conclude that terminal deoxynucleotidyl transferase is a biochemical marker that will be useful in the study of lymphoma.

Morphological changes in the lymphoid organs induced by diphenylhydantoin sodium (DPH)

In rats injected with DPH the morphological changes induced in the thymus and lymph nodes were studied. In the thymus, features suggesting block of cellular differentiation were found, and in lymph nodes depletion of the paracortical zone and intense plasma cell hyperplasia could be observed. The correlation of these findings with the functional changes in the immunological response induced by the drug, and the possible implications of these changes in the induction of lymphoma are discussed.