Porcine articular cartilage from cases of experimentally induced Erysipelas polyarthritis, a comparative model of rheumatoid arthritis (RA) in man, was examined with different histological and immunohistochemical techniques. The preexisting canals in articular cartilage played a crucial role during the flooding and deposition of arthritogenic microorganisms deep into the cartilage matrix. Subsequently this vascularized tissue mediated the same inflammatory reactions in hyaline cartilage of young animals as seen in other connective tissues. However, these stereotypical responses to injury were modulated by the unique composition and structure of articular cartilage.

In experimentally-induced erysipelas polyarthritis, preexisting cartilage canals in articular cartilage play a crucial role during the very onset of the disease. This observation might have some implications for the pathogenesis of other infectious arthritides in young animals or even rheumatoid arthritis in man.

Porcine articular cartilage from cases of experimentally induced Erysipelas arthritis was examined with different histological techniques and by electron microscopy. A small percentage of specimens of osteoarthritic cartilage revealed an interlacunar network in the extracellular matrix. These "matrix-streaks" showed characteristic features of densely packed fibrillar elements and collagenous fibrils, as narrow bands connecting adjacent chondrocytes. In a given cartilage site the network had a constant pattern. It is hypothesized that the network formation is correlated with altered joint metabolism and represents regressive changes in cartilage matrix as a result of external mechanical forces. Using a variety of methods, the possibility of the network being an artifact of histological processing could virtually be ruled out. As there are so far only few and contradictory reports on the interlacunar network of articular cartilage, its precise biological significance remains to be established.

Summary Immunohistological and enzyme‐cytochemical investigations were carried out to identify and characterize lymphocyte subpopulations in situ in the pig. Using a specific antiserum, T lymphocytes could be demonstrated chiefly in the thymus, the paracortex of lymph nodes and the periarteriolar lymphocytic sheath of the splenic white pulp. Complement‐receptor‐positive cells were mainly located in follicles and the marginal zone, whereas Fc‐IgM receptors could be demonstrated on corona lymphocytes of the follicles, on cells of the marginal zone of the white pulp and concentrated around sheathed capillaries. The main location of B‐cell subpopulations of the IgG and IgM isotype, respectively, were the marginal zones and the follicles. Surface immunoglobulin expressing B lymphocytes and plasma cells were predominantly of the IgM isotype. The IgG within the follicles was mainly of non‐endogenous origin. Histochemically, ANAE may serve in some respects as a suitable marker for the differentiation of porcine T and B lymphocytes. The functional division of the immune system in the pig correlates anatomically to some extent with T‐ and B‐cell compartments in the lymphoid organs. Apart from the inverted microanatomy of the lymph node, the porcine lymphoreticular tissue corresponds to equivalent structures of other mammalian species investigated. Zusammenfassung Immunologische und enzymhistochemische Identifizierung von Lymphozyten‐Subpopulationen in lymphoretikulären Geweben des Schweines Es wurden immunhistologische und enzymzytochemische Untersuchungen durchgeführt, um Lymphozyten‐Subpopulationen beim Schwein in situ zu identifizieren und zu charakterisieren. Mit Hilfe eines spezifischen Antiserums konnten T‐Lymphozyten hauptsächlich im Thymus, dem Parakortex des Lymphknotens und in der periarteriolären lymphatischen Scheide der weißen Milzpulpa nachgewiesen werden. Komplementrezep‐torpositive Zellen waren besonders in den Follikeln und der Marginalzone zu finden; dagegen konnten Fc‐IgM‐Rezeptoren vorzugsweise auf Lymphozyten der Follikelmantelzone, auf den Zellen der Marginalzone der weißen Pulpa und konzentriert um die Hülsenkapillaren demonstriert werden. Das Hauptverteilungsgebiet der B‐Zellsubpopulationen vom IgG‐ bzw. IgM‐Isotyp waren die Marginalzonen und die Follikel. Die Immunglobuline auf den B‐Lymphozyten und in den Plasmazellen gehorten vornehmlich der IgM‐Klasse an. Das IgG in den Follikeln war hauptsächlich nichtendogener Herkunft. Histochemisch kommt in gewisser Weise nur ANAE als geeigneter Marker zur Differenzierung von porcinen T‐ und B‐Lymphozyten in Betracht. Beim Schwein korreliert die funktionelle Aufteilung des Immunsystems weitgehend mit der anatomischen T‐ und B‐Zellkompartimentierung in den lymphatischen Organen. Abgesehen von der inversen Mikroanatomie des Lymphknotens entspricht der Aufbau des lymphoretikulären Gewebes des Schweines dem der anderen bereits untersuchten Säugetierarten. Résumé Identification immunologique et enzymo‐histochimique de sous‐populations lymphocytaires dans des tiss...

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