Non‐Hodgkin's lymphomas: An immunohistochemical and histological study

Abstract

Immunohistochemical and histoogical studies have been performed on paraffin sections of 19 cases of non-Hodgkin's lymphoma (NHL). All the cases were lymphocytic in type and, on the basis of the National Lymphoma Investigation classification, 11 were follicular (six small, three mixed small and large, and two large cell types) and eight were diffuse (four intermediate, three poorly and one well-differentiated types). Marshall's metalophil method revealed a population of dendritic histiocytes in and around the follicles of follicular lymphomas. The distribution of the dendritic cells within the neoplastic follicles resembled the distribution of similar cells in reactive follicles, lending support to the concept of an origin for lymphoma follicles from their reactive counterparts. In the diffuse lesions the dendritic cells were large and more pleomorphic than in the follicular lesions, but these features were not so pronounced as those previously observed in Hodgkin's disease. The PAP sequence was used to demonstrate Ig, and as judged by the types of light and heavy chains in the lymphoma cells, the cases were divided into three groups: Group 1 (eight cases) in which the lymphoma cells contained monotypic Ig; Group 2 (six cases) in which monotypic Ig was probably present; and Group 3 (four cases) where no evidence of monotypic Ig secretion was found. Monotypic Ig was most commonly found in follicular lymphomas, mu kappa secretion being the most frequently identified combination of heavy and light chains. The majority of cases (73 per cent.) were thus clearly derived from B lymphocytes. However, the fact that monoclonality was evident in only a proportion of cases suggested that lymphomas may be polyclonal initially and proportion of cases suggested that lymphomas may be polyclonal initially and that monoclonality is a later development. In addition to the lymphoma cells, normal mature plasma cells containing a high concentration of intracellular Ig were present in all but one of the lesions. The Ig was polytypic, cells containing kappa and lambda chains being present in roughly equal numbers and gamma chains pre-dominating. Extracellular Ig (gamma, mu, kappa, lambda) was also present in many lesions. Collections of small non-lymphomatous lymphocytes were also present in all cases. In eight lesions these appeared to have polytypic surface Ig (mu, kappa, lambda). Dendritic cells mingled with these lymphocytes. Collections of small lymphocytes non-reactive for Ig were also present. These had no association with dendritic histiocytes and might have been T cells. It is concluded that in most cases immunohistochemistry alone provides an insufficient basis for the diagnosis of lymphoma and that disturbance of cellular morphology and tissue architecture remain the most useful criteria on which the diagnosis of lymphoma rests.