E Horst

A recently described splice variant of CD44 expressed in metastasizing cell lines of rat tumors, has been shown to confer metastatic potential to nonmetastasizing rat pancreatic carcinoma and sarcoma cell lines. Using antibodies raised against a bacterial fusion protein encoded by variant CD44 sequences, we have explored the expression of variant CD44 glycoproteins on human lymphoid cells and tissues and on non-Hodgkin's lymphomas. Normal lymphohematopoietic cells express barely detectable low levels of variant CD44 glycoproteins, whereas T lymphocytes, upon activation by mitogen or antigen, transiently upregulate expression of specific CD44 variant glycoproteins. The reaction pattern of various antibodies indicates that these CD44 variants contain the domain encoded by exon v6, which is part of the variant that in the rat confers metastatic capability. It is interesting that overexpression of v6 was also found in several aggressive, but not low-grade, non-Hodgkin's lymphomas.

AIMS: Monocytes are critical mediators of healing following acute myocardial infarction (AMI), making them an interesting target to improve myocardial repair. The purpose of this study was a gain of insight into the source and recruitment of monocytes following AMI in humans. METHODS AND RESULTS: Post-mortem tissue specimens of myocardium, spleen and bone marrow were collected from 28 patients who died at different time points after AMI. Twelve patients who died from other causes served as controls. The presence and localization of monocytes (CD14(+) cells), and their CD14(+)CD16(-) and CD14(+)CD16(+) subsets, were evaluated by immunohistochemical and immunofluorescence analyses. CD14(+) cells localized at distinct regions of the infarcted myocardium in different phases of healing following AMI. In the inflammatory phase after AMI, CD14(+) cells were predominantly located in the infarct border zone, adjacent to cardiomyocytes, and consisted for 85% (78-92%) of CD14(+)CD16(-) cells. In contrast, in the subsequent post-AMI proliferative phase, massive accumulation of CD14(+) cells was observed in the infarct core, containing comparable proportions of both the CD14(+)CD16(-) [60% (31-67%)] and CD14(+)CD16(+) subsets [40% (33-69%)]. Importantly, in AMI patients, of the number of CD14(+) cells was decreased by 39% in the bone marrow and by 58% in the spleen, in comparison with control patients (P = 0.02 and <0.001, respectively). CONCLUSIONS: Overall, this study showed a unique spatiotemporal pattern of monocyte accumulation in the human myocardium following AMI that coincides with a marked depletion of monocytes from the spleen, suggesting that the human spleen contains an important reservoir function for monocytes.

Lymphocyte traffic into lymph nodes and into mucosa-associated lymphoid tissues is regulated by specialized postcapillary high endothelial venules (HEVs). The authors have produced a rat monoclonal antibody, HECA-452, that detects a human endothelial cell differentiation antigen selectively expressed on high endothelium. In immunoperoxidase studies, HECA-452 intensely stains all HEVs within lymphoid organs. In normal nonlymphoid tissues the antibody stains no vascular endothelium. The antibody, in addition to reacting with high endothelium, cross-reacts with a set of monocytic cells. In pathologic states such as autoimmune thyroiditis and Crohn's disease, known for the development of dense, frequently organized, lymphocytic infiltrates, HECA-452 detects HEV-like vessels containing luminal and intramural lymphocytes, presumably in the process of extravasating. The antigen was not expressed at detectable levels by venules in less heavily infiltrated chronic inflammatory sites nor in acutely inflamed tissues. In lymphoid malignancies, the only vessels stained were morphologically characteristic HEVs in association with areas of residual normal lymphoid tissue or reactive lymphocytic infiltrates. The specificity of HECA-452 for high endothelial cells confirms the highly specialized nature of these vessels and will permit studies of the regulation of high endothelial cell differentiation in vivo and in vitro. The HECA-452 antigen is preserved in paraffin sections of sublimate formaldehyde- and also routinely formalin-fixed tissues. Thus, HECA-452 will be widely applicable for the immunohistologic detection of endothelium specialized for the support of highly increased lymphocyte extravasation in inflammatory sites.

Adhesive interactions between lymphocyte cell-surface receptors and components of the vascular endothelium and the extracellular matrix play an important role in the control of lymphocyte migration and homing. To investigate whether lymphocyte adhesion molecules involved in the migration of normal lymphocytes, i.e., CD44 homing receptor, LFA-1 (CD11a/18), and ICAM-1 (CD54), also play a role in the spread and hence in the disease course of non-Hodgkin's lymphomas (NHL), expression of these molecules was examined in 78 cases of diffuse large-cell lymphoma. Other potential risk factors considered in this study were sex, age, primary tumor localization, lineage (T cell vs. B cell), and histopathological subtype. 27 of 53 (51%) patients with a lymphoma having a high CD44 antigen expression showed tumor spread beyond stage II at diagnosis while this was the case in only three of 25 (12%) patients with lymphomas that were CD44 low/negative (chi-square 25.4, p less than 0.001). Similarly, poor response to treatment, i.e., absence of remission or relapse, and or death from lymphoma, was more common among patients with lymphomas expressing high levels of CD44; actuarial survival among patients with CD44 high and low lymphomas was 47% and 91%, respectively (Mantel-Cox 6.1, p = 0.02). Neither LFA-1 nor ICAM-1 expression showed a significant correlation to lymphoma dissemination or disease course. Of the other factors considered, T cell phenotype was associated with an unfavorable prognosis while nodal localization was a risk factor for dissemination. Taken together, our findings suggest that CD44 antigen expression plays an important role in the dissemination of NHL and via this mechanism exerts an unfavorable prognostic influence.

T cell autoreactivity is a hallmark of autoimmune diseases but can also benefit self-maintenance and foster tissue repair. Herein, we investigated whether heart-specific T cells exert salutary or detrimental effects in the context of myocardial infarction (MI), the leading cause of death worldwide. After screening more than 150 class-II-restricted epitopes, we found that myosin heavy chain alpha (MYHCA) was a dominant cardiac antigen triggering post-MI CD4+ T cell activation in mice. Transferred MYHCA614-629-specific CD4+ T (TCR-M) cells selectively accumulated in the myocardium and mediastinal lymph nodes (med-LN) of infarcted mice, acquired a Treg phenotype with a distinct pro-healing gene expression profile, and mediated cardioprotection. Myocardial Treg cells were also detected in autopsies from patients who suffered a MI. Noninvasive PET/CT imaging using a CXCR4 radioligand revealed enlarged med-LNs with increased cellularity in MI-patients. Notably, the med-LN alterations observed in MI patients correlated with the infarct size and cardiac function. Taken together, the results obtained in our study provide evidence showing that MI-context induces pro-healing T cell autoimmunity in mice and confirms the existence of an analogous heart/med-LN/T cell axis in MI patients.