Characterization of extracellular matrix in non-Hodgkin's lymphomas

Basement membrane proteins laminin, type IV collagen and aminoterminal propeptide of type III collagen (type III pN-collagen) are important components of extracellular matrix of normal lymph nodes; they are present in reticular fibres and in the walls of blood vessels and sinuses. We have studied the distribution of these proteins in 45 cases of non-Hodgkin's lymphomas representing different types of Kiel classification. Light microscopic immunohistochemistry was used on sections from formalin fixed, paraffin embedded biopsy specimens. Reticular cells were identified by using antibodies against S-100 protein, a marker for dendritic and interdigitating reticulum cells, and against cystatin A for the demonstration of follicular dendritic reticulum cells. The findings of the immunohistochemical stainings were generally similar in the different lymphoma types. Thus the method for the demonstration of extracellular matrix proteins could not give obvious aid for lymphoma classification. BM stainings proved to be efficient in the demonstration of sinuses. Marginal and medullary sinuses of the nodal cases were either totally or partly spared and open also in the cases in which there was extracapsular growth. The fibre content was variable, but generally the distribution of all the three extracellular matrix proteins was comparable with each other and mainly corresponded with the pattern seen in conventional Gomori's reticulin stain. This also holds for the tumor tissue infiltrated through the capsule and for extranodal cases. Areas of sclerosis of some cases contained only type III pN-collagen. Reticular fibres were at places seen to be closely associated with cells of spindle or dendritic shape. A few reticulum cells could be found to show cytoplasmic staining for laminin, type IV collagen and type III pN collagen. This finding suggests that the cells are synthetizing these proteins. The amount of cells staining for cystatin A or S-100 protein did not generally correlate with the amount of fibres, and most of the stained cells were not closely associated with fibres. The results show that in non-Hodgkin's lymphomas basement membrane proteins and type III pN-collagen are important components of reticular fibres. Results also indirectly support the main role of fibroblastic reticulum cells in the production of the fibres.