Diversity of cell phenotypes among MT-2 cell lines affects the growth of U937 cells and cytokine production

HTLV-1-infected cells drive the differentiation of monocytes into macrophages in vitro

BACKGROUND

The human T-cell lymphotropic virus type 1 (HTLV-1) is a retrovirus that causes HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). HAM/TSP is a chronic inflammatory neurodegenerative disease characterized by leukocyte infiltration in the spinal cord. T-lymphocytes are the most important targets of HTLV-1 infection, but monocytes are also infected. Monocytes from HTLV-1-infected individuals exhibit important functional differences compared to cells from uninfected donors. Here, we investigated the effects of cell-cell physical contact and/or secreted factors of HTLV-1-infected cells in monocyte activation and differentiation.

METHODS

The THP-1 human monocytic cell line was co-cultured with a human cell line transformed by HTLV-1 (MT-2) for 6 days. To determine the effects of co-culturing HTLV-1-infected cells in THP-1 monocytes cells were characterized by flow cytometry, immunofluorescence microscopy, and real-time PCR. Computational analysis of published transcriptomic datasets was realized to compare molecular profiles of macrophages and mononuclear cells from HTLV-1 carriers.

RESULTS

Co-culture of monocytes with HTLV-1-infected cells induced macrophage differentiation and upregulation of typical macrophages-associated molecules (HLA-DR, CD80, and CD86), increased cytokine (TNFα, IL-6, and IL-1β) levels and their coding genes expression. Consistently, published transcriptomic datasets showed changes in important genes associated with inflammation during HAM/TSP in patients. The presence of HTLV-1-infected cells in the culture also induced significant upregulation of Interferon Stimulated Genes (ISG), indicating viral infection. Monocyte activation and differentiation into pro-inflammatory macrophages occurred in a cell-to-cell contact-independent manner, suggesting the role of factors secreted by infected cells.

CONCLUSIONS

Together, our results indicated that HTLV-1-infected cells induced monocyte differentiation into macrophages inflammatory, predominantly.

Effect of HTLV-1 Infection on the Clinical Course of Patients with Rheumatoid Arthritis

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The effects of HTLV-1 on health are not fully elucidated. Epidemiological studies have shown that the prevalence of HTLV-1 infection is high in patients with rheumatic diseases. The prevalence of comorbidities, such as Sjögren’s syndrome and rheumatoid arthritis (RA), is higher in patients with HAM/TSP than the in general population. Studies have shown the effects of HTLV-1-infection on the clinical course of RA. Major questions on the association between HTLV-1 infection and RA: (1) Is it possible that HTLV-1 infection causes RA? (2) Do patients with RA who are infected with HTLV-1 have different clinical features? (3) Are immunosuppressants associated with an increased prevalence of HAM/TSP or ATL in RA patients with HTLV-1 infection? Is ATL an immunosuppressive therapy-associated lymphoproliferative disorder? No large-scale studies have investigated the incidence of ATL in patients with RA. However, several studies have reported the development of ATL in patients with RA who have HTLV-1 infection. This review aimed to shed light on the association between HTLV-1 infection and RA and summarize the unmet medical needs of RA patients with HTLV-1 infection.

In vitro Evaluation of the Safety of Adalimumab for the Eye Under HTLV-1 Infection Status: A Preliminary Study

Adalimumab (ADA), a fully human monoclonal tumor necrosis factor (TNF)-α antibody, is one of the most widely used biologics in the treatment of inflammatory diseases. However, ADA can exacerbate infectious conditions, induce paradoxical reactions such as inflammation, and cause neoplasia. Human T-cell leukemia virus type 1 (HTLV-1) is an infectious agent that induces inflammation and neoplastic infiltration in the eye. To date, numerous HTLV-1 carriers have been treated with adalimumab to suppress inflammation out of necessity, when standard anti-inflammatory drugs such as steroids and immunosuppressive agents have proven inadequate to control the inflammation. Here, we clarify the safety of adalimumab for the eye under HTLV-1 infectious conditions in vitro. We used the adult retinal pigment epithelial cell line (ARPE)-19 cell line as ocular resident cells, and used MT2 and TL-Om1 as HTLV-1-infected cells. ARPE-19 and MT2/TL-Om1 were co-cultured, and then adalimumab was administered. Production of cytokines and chemokines, TNF-α receptor (TNF-R), HTLV-1 proviral load (PVL), and apoptosis were measured to assess the effects of adalimumab. Contact between ARPE-19 and MT2/TL-Om1 produced inflammatory cytokines such as TNF, interleukin (IL)-6, IL-8 and IL-10, and transduced chemokines such as interferon-inducible protein-10 (IP-10), monocyte chemotactic protein-1 (MCP-1), monokine induced by interferon-γ (MIG), and regulated on activation, normal T cell expressed and secreted (RANTES). No inflammatory cytokines and chemokines were exacerbated by adalimumab. Expression of TNF-R on ARPE-19 and MT2/TL-Om1 cells, HTLV-1 PVLs of MT2/TL-Om1 cells, and cell growth rate and apoptotic rate of ARPE-19 were unaffected by adalimumab. In conclusion, adalimumab does not appear to exacerbate HTLV-1-associated inflammatory conditions in the eye or increase PVL in HTLV-1-infected T cells. These data suggest that adalimumab could be used safely for the eye under HTLV-1 infectious conditions from the perspective of in vitro assessment.