Effects of alveolar surfactant aggregates on T-lymphocyte proliferation

Impact of the New Generation Reconstituted Surfactant CHF5633 on Human CD4+ Lymphocytes

Background

Natural surfactant preparations, commonly isolated from porcine or bovine lungs, are used to treat respiratory distress syndrome in preterm infants. Besides biophysical effectiveness, several studies have documented additional immunomodulatory properties. Within the near future, synthetic surfactant preparations may be a promising alternative. CHF5633 is a new generation reconstituted synthetic surfactant preparation with defined composition, containing dipalmitoyl-phosphatidylcholine, palmitoyl-oleoyl-phosphatidylglycerol and synthetic analogs of surfactant protein (SP-) B and SP-C. While its biophysical effectiveness has been demonstrated in vitro and in vivo, possible immunomodulatory abilities are currently unknown.

Aim

The aim of the current study was to define a potential impact of CHF5633 and its single components on pro- and anti-inflammatory cytokine responses in human CD4⁺ lymphocytes.

Methods

Purified human CD4⁺ T cells were activated using anti CD3/CD28 antibodies and exposed to CHF5633, its components, or to the well-known animal-derived surfactant Poractant alfa (Curosurf^®). Proliferative response and cell viability were assessed using flow cytometry and a methylthiazolyldiphenyltetrazolium bromide colorimetric assay. The mRNA expression of IFNγ, IL-2, IL-17A, IL-22, IL-4, and IL-10 was measured by quantitative PCR, while intracellular protein expression was assessed by means of flow cytometry.

Results

Neither CHF5633 nor any of its phospholipid components with or without SP-B or SP-C analogs had any influence on proliferative ability and viability of CD4⁺ lymphocytes under the given conditions. IFNγ, IL-2, IL-17A, IL-22, IL-4, and IL-10 mRNA as well as IFNγ, IL-2, IL-4 and IL-10 protein levels were unaffected in both non-activated and activated CD4⁺ lymphocytes after exposure to CHF5633 or its constituents compared to non-exposed controls. However, in comparison to Curosurf^®, expression levels of anti-inflammatory IL-4 and IL-10 mRNA were significantly increased in CHF5633 exposed CD4⁺ lymphocytes.

Conclusion

For the first time, the immunomodulatory capacity of CHF5633 on CD4⁺ lymphocytes was evaluated. CHF5633 did not show any cytotoxicity on CD4⁺ cells. Moreover, our in vitro data indicate that CHF5633 does not exert unintended pro-inflammatory effects on non-activated and activated CD4⁺ T cells. As far as anti-inflammatory cytokines are concerned, it might lack an overall reductive ability in comparison to animal-derived surfactants, potentially leaving pro- and anti-inflammatory cytokine response in balance.

Pulmonary surfactant: an immunological perspective

Pulmonary surfactant has two crucial roles in respiratory function; first, as a biophysical entity it reduces surface tension at the air water interface, facilitating gas exchange and alveolar stability during breathing, and, second, as an innate component of the lung's immune system it helps maintain sterility and balance immune reactions in the distal airways. Pulmonary surfactant consists of 90% lipids and 10% protein. There are four surfactant proteins named SP-A, SP-B, SP-C, and SP-D; their distinct interactions with surfactant phospholipids are necessary for the ultra-structural organization, stability, metabolism, and lowering of surface tension. In addition, SP-A and SP-D bind pathogens, inflict damage to microbial membranes, and regulate microbial phagocytosis and activation or deactivation of inflammatory responses by alveolar macrophages. SP-A and SP-D, also known as pulmonary collectins, mediate microbial phagocytosis via SP-A and SP-D receptors and the coordinated induction of other innate receptors. Several receptors (SP-R210, CD91/calreticulin, SIRPalpha, and toll-like receptors) mediate the immunological functions of SP-A and SP-D. However, accumulating evidence indicate that SP-B and SP-C and one or more lipid constituents of surfactant share similar immuno-regulatory properties as SP-A and SP-D. The present review discusses current knowledge on the interaction of surfactant with lung innate host defense.

Therapeutic use of surfactant components in allergic asthma

Pulmonary surfactant is a complex mixture of lipids and proteins that reduces the surface tension at the air-liquid interface. In addition to its biophysical function, some surfactant components play an important role for the innate and adaptive immunity of the lung. A negative modulation of the surfactant function was observed in allergic asthma leading to the assumption that the therapeutic application of surfactant components might be beneficial in this disease. So far, there are a number of preclinical and already some clinical studies demonstrating various effects of different surfactant components that were administered with preventive or therapeutic aim in allergic asthma. This review summarizes the current knowledge on the possibilities to treat allergic asthma with surfactant components.

T‐cell memory and recall responses to respiratory virus infections

The respiratory tract is characterized by its large surface area and the close association of an extensive vasculature with the external environment. As such, the respiratory tract is a major portal of entry for many pathogens. The immune system is able to effectively control most pulmonary pathogens and establish immunological memory that is capable of mediating an accelerated and enhanced recall response to secondary pathogen challenge. A key component of the recall response in the lung involves the rapid response of antigen-specific memory CD8+ T cells. Recent studies have shown that memory CD8+ T cells are extremely heterogeneous in terms of phenotype, function, anatomical distribution, and longevity. However, we have little understanding of how the different subsets of memory cells actually contribute to the recall response, especially with respect to peripheral or mucosal sites, such as the lung. Since immunological memory is the cornerstone of vaccination, it is essential that we understand how different memory CD8+ T-cell subsets are initially generated, maintained over time, and contribute to recall responses. This review focuses on memory T cells that mediate recall responses to influenza and parainfluenza virus infections in the lung.

Surfactant protein A increases matrix metalloproteinase-9 production by THP-1 cells

Matrix metalloproteinase (MMP)-9 from alveolar macrophages is a major source of elastolytic activity in the lung. It is increased in the bronchoalveolar lavage fluid of patients with emphysema. Although the importance of macrophage-derived elastolytic activity in the pathogenesis of emphysema is well established, questions remain about MMP-9 regulation and activity. Because surfactant protein A (SP-A) is capable of modulating other functions of human monocytic cells, we hypothesized that SP-A may regulate MMP-9 expression. Vitamin D3-differentiated THP-1 cells and peripheral blood mononuclear cells were stimulated in vitro with several concentrations of SP-A for different incubation times. MMP-9 mRNA expression was measured by dot-blot analysis, gelatinolytic activity in the medium was determined by gel zymography, protein expression was determined by ELISA, and a specific MMP-9 activity assay was used to measure the state of activation of this enzyme in the cell supernatants. SP-A induced the expression of MMP-9 in both cell types, the effect was time and dose dependent, and MMP-9 was released in its zymogen form. On the basis of results of neutralizing antibody studies, we believe that SP-A action is mediated through Toll-like receptor-2. Even though the biological meaning of these findings remains to be elucidated, these observations suggest the presence of a novel, locally controlled mechanism by which MMP-9 levels may be regulated in alveolar macrophages. We speculate that SP-A may influence the protease/antiprotease balance in the lungs of patients with quantitative and/or qualitative changes in surfactant constituents favoring an abnormal breakdown of extracellular matrix components.

Cutting Edge: Effector Memory CD8+ T Cells in the Lung Airways Retain the Potential to Mediate Recall Responses

Previous studies have shown that long-lived memory CD8(+) T cells persist in the lung airways following the resolution of a murine Sendai virus infection. These cells are CD11a(low), noncytolytic, and do not proliferate in the lung airways raising the possibility that they are "end stage" or terminally differentiated memory cells. In this current report, we investigated the functional characteristics of these cells by analyzing their capacity to respond to secondary viral infection outside of the lung environment. We show that, after transfer into the bloodstream, CD11a(low) memory T cells from the lung airways can return to the secondary lymphoid tissue and respond to a secondary viral challenge. Furthermore, these cells re-express CD11a, which may contribute to their migratory and proliferative capacity. These data demonstrate that lung airway memory CD8(+) T cells are not terminally differentiated cells and retain the capacity to mediate recall responses to infection.