Benign and malignant proliferative response. Dermal infiltration, origin and importance.

Lymphoreticular infiltration (LRI) is the most common type of dermal infiltration. The LRI is made up of two main components: (i) a dermal skeleton, and (ii) the infiltration in a strict sense. (i) The dermal skeleton consists of the blood vessel involved, most probably a post-capillary venule, and activated fibroblasts (Fig. 3). The activated fibroblasts contain "paraplasmatic granules" in their processes (Fig. 4). Since the fibroblasts are in mutual contact by their ramifications (Fig. 3), they are reticulum cells by definition (Bessis). In our opinion they are the only local reticulum cells in the dermis. They are not stem cells, nor do they belong to the reticulo-endothelial system and they do not give rise to histiocytes. (ii) In the skeleton of LRI, other cells infiltrate, predominantly monocytes and lymphocytes. The LRI may specialize and contain various amounts of neutrophilic, basophilic, or eosinophilic leukocytes and plasma cells. If enough B-lymphocytes and plasmacells are involved, abnormal globulins may be produced (e.g. syphilis II). The lymphomas are considered to be malignant proliferative disorders of LRI-type. LRI is found in allergic spreading reactions mediated by stimulated lymphocytes. A similar spreading of lymphocytes is to be expected if the allergen sensitizes a lymphocyte with neoplastic information (e.g. tumor virus) (Fig. 6). The degree of dedifferentiation and the response of the organism to the dedifferentiated lymphocytes is the reason for the variety of lymphomas.