Immunoelectron-microscopic investigations of lymph nodes

Castleman's disease. Differences in follicular dendritic network in the hyaline vascular and plasma cell variants

Twenty-seven cases of the hyaline vascular variant and 10 cases of the plasma cell variant of Castleman's disease were studied with the paraffin resistant monoclonal antibodies Ki-FDC1p and/or Ki-M4p against follicular dendritic cells. Studies with the monoclonal antibody Ki-M9, for the detection of sinus lining cells, were also performed on the available frozen tissue in four cases of the hyaline vascular variant. In nine of the 10 plasma cell variant cases, the predominant type of follicular dendritic cell network was similar to that seen in normal or reactive germinal centres. In contrast, the hyaline vascular variant demonstrated either an expanded, disrupted, follicular dendritic cell network (10 cases) or multiple tight collections of follicular dendritic cells (16 cases). Sinus lining cells were not detected in the four cases studied. The difference in the predominant type of dendritic meshwork is an additional distinguishing feature to separate the plasma cell and hyaline vascular variants of Castleman's disease. The patterns of dendritic network seen in the hyaline vascular type, together with the absence of sinus lining cells, appear to favour the hamartoma theory proposed for this variant.

Follicular dendritic cells in extranodal non-Hodgkin lymphomas of MALT and non-MALT type

Extranodal lymphomas of the thyroid (n = 19), kidney (n = 15) and testis (n = 30) were investigated histologically and immunohistochemically for follicular dendritic cell pattern using the monoclonal antibody Ki-FDClP. This recognizes follicular dendritic cells in paraffin sections. Follicular dendritic cells were most predominant in lymphomas of the thyroid. These thyroid lymphomas showed the morphological features of mucosa-associated lymphoid tissue (MALT) type lymphomas in 18 of 19 cases and were classified as high-grade malignant lymphoma of MALT type with evidence of a low-grade malignant component (n = 18). Ten of these cases contained destroyed reactive follicles of follicular dendritic cells. In 6 of these 10 cases follicular dendritic cells occurred in a pattern of tumour-associated abortive follicle type. The remaining lymphoma of the thyroid was an immunoblastic lymphoma of B-cell type showing no detectable follicular dendritic cells. In extranodal lymphomas of non-MALT type follicular dendritic cells occurred in only two cases where immunocytoma involved the kidney. Malignant lymphomas of the kidney (chronic lymphocytic leukaemia, n = 2; immunocytoma, n = 4; centroblastic lymphoma, n = 9) and of the testis (immunocytoma, n = 2; centroblastic lymphoma, n = 27; immunoblastic lymphoma of B-cell type, n = 1) revealed no characteristics of MALT type lymphoma, cytologically or with respect to follicular dendritic cells. Classical lymphoepithelial lesions formed by centrocyte-like cells, a hallmark of MALT, occurred exclusively in thyroid lymphomas of MALT type. Although occurrence of classical lymphoepithelial lesions formed by centrocyte-like cells was limited to thyroid lymphomas of MALT type, a growth pattern of lymphoid blasts, with formation of lesions mimicking lymphoepithelial lesions superficially, was found in 6 of 27 testicular centroblastic lymphomas. Follicular dendritic cells in non-Hodgkin's lymphomas of MALT type show distinct follicular patterns not found in other extranodal lymphomas such as those found in the kidney and testis.