3D examination reveals increased destruction of alpha-actin-positive structures in advanced follicular lymphoma stages

Abstract

Follicular lymphoma (FL) represents the most prevalent subtype of non-Hodgkin’s-lymphoma in Western Europe and the United States. While the examination of two-dimensional histological slides remains the gold standard method for diagnosing FL stages, three-dimensional analysis provides additional insights, particularly regarding cellular morphology, spatial relationships and network connectivity. This investigation assessed the tumor-related morphological destruction of fibroreticular cell (FRC) networks bordering germinal centres in FL. A confocal laser scanning technology and a digital three-dimensional analysis system were used. Quantitive measurements included the length of fibroblastic reticular walls surrounding the germinal centres as well as the size of the gaps and holes within these structures. Three-dimensional analysis revealed progressive structural degradation and a reduction in mechanical barrier integrity, with differences observed between low- and high-grade FL. High-grade FL exhibited greater network destruction. Fibroblastic reticular cell networks’ wall length demonstrated a consistent decline across all grades. The lengths of these walls and wall-like structures in FL grades 1 or 2 were similar to reactive germinal centres seen in lymphadenitis, as well as the gap size. The gaps are thought to be responsible for B- and T-cell exchange. This work demonstrated the massive destruction of neoplastic germinal centres in grades 3a and 3b FL. In grade 3b, this was accompanied by a likely dysfunctional mechanical border of the germinal centre and the near-complete loss of structural integrity. Under physiological conditions, gaps and holes regulate lymphoid traffic. Under reactive conditions, only a few specific T-cells can access the germinal centre. Under neoplastic conditions, the diameter of these gaps increases as grades increase, culminating in complete structural disruption in grade 3b. The mechanical destruction was found to begin at one pole of the germinal centre, as evidenced by localized decay and fragmentation of FRC walls on one side. Fibroblastic reticular cell networks are critical for maintaining chemokine gradients to ensure compartmentalisation of lymphoid structures. Their ongoing degradation in FL of the networks leads to a morphological loss of function. This is due to the blurring of various lymph node zones.