Effects of cryopreservation of immune responses. XI. Heightened secretion of tumor necrosis factor-alpha by frozen human peripheral blood mononuclear cells

Biomolecular Pathways of Cryoinjuries in Low-Temperature Storage for Mammalian Specimens

Low-temperature preservation could effectively extend in vitro storage of biological materials due to delayed or suspended cellular metabolism and decaying as illustrated by the Arrhenius model. It is widely used as an enabling technology for a variety of biomedical applications such as cell therapeutics, assisted reproductive technologies, organ transplantation, and mRNA medicine. Although the technology to minimize cryoinjuries of mammalian specimens during preservation has been advanced substantially over past decades, mammalian specimens still suffer cryoinjuries under low-temperature conditions. Particularly, the molecular mechanisms underlying cryoinjuries are still evasive, hindering further improvement and development of preservation technologies. In this paper, we systematically recapitulate the molecular cascades of cellular injuries induced by cryopreservation, including apoptosis, necroptosis, ischemia-reperfusion injury (IRI). Therefore, this study not only summarizes the impact of low-temperature preservations on preserved cells and organs on the molecular level, but also provides a molecular basis to reduce cryoinjuries for future exploration of biopreservation methods, materials, and devices.

An In Vitro Model for Measuring Immune Responses to Malaria in the Context of HIV Co-infection

Malaria and HIV co-infection is a growing health priority. However, most research on malaria or HIV currently focuses on each infection individually. Although understanding the disease dynamics for each of these pathogens independently is vital, it is also important that the interactions between these pathogens are investigated and understood. We have developed a versatile in vitro model of HIV-malaria co-infection to study host immune responses to malaria in the context of HIV infection. Our model allows the study of secreted factors in cellular supernatants, cell surface and intracellular protein markers, as well as RNA expression levels. The experimental design and methods used limit variability and promote data reliability and reproducibility. All pathogens used in this model are natural human pathogens (Plasmodium falciparum and HIV-1), and all infected cells are naturally infected and used fresh. We use human erythrocytes parasitized with P. falciparum and maintained in continuous in vitro culture. We obtain freshly isolated peripheral blood mononuclear cells from chronically HIV-infected volunteers. Every condition used has an appropriate control (P. falciparum parasitized vs. normal erythrocytes), and every HIV-infected donor has an HIV uninfected control, from which cells are harvested on the same day. This model provides a realistic environment to study the interactions between malaria parasites and human immune cells in the context of HIV infection.

Induced cytokine response of human PMBC-cultures: correlation of gene expression and secretion profiling and the effect of cryopreservation

The immune system is regulated by the complex interaction of multiple cytokines, which are secreted signaling molecules affecting other cells. In this work, we studied the cytokine response to several well-known stimulants, such as OKT-3, Con A, PWM, and SEB. Healthy donor cells (PBMCs) were cultivated for up to 72 h and the mRNA levels and cytokine release of four key cytokines (IL-2, IL-4, IFN-γ, and TNF-α) were analyzed by RT-PCR and bead-based multiplex analyses. The generated cytokine profiles showed characteristic expression patterns and secretion kinetics for each cytokine and substance. PWM/SEB and OKT-3 led to a very fast and long-lasting immune response, whereas Con A induced the slowest cytokine production. Cytokine concentrations also differed greatly. The highest IFN-γ concentration was 1000 times higher than the respective IL-4 concentration. Gene expression and cytokine concentration profiles were strongly correlated during the time course. The chronological response of the donors' cytokine profiles coincided, but showed individual characteristics regarding the strength of the cytokine release. The comparison of stimulation experiments using freshly isolated and cryopreserved PBMCs showed that, for the observation of an immunological response at early points in time, gene expression experiments are more reliable than the measurement of cytokines in the cell culture supernatant. However, the freezing of cells influences the response significantly. The measurement of secreted proteins is the superior method at later points in time.

A flow cytometric method to assess antigen-specific proliferative responses of different subpopulations of fresh and cryopreserved human peripheral blood mononuclear cells

We have used PKH26 dye, which is incorporated stably into the membrane of cells, to determine, using flow cytometry, lymphocyte proliferative responses to the antigen tetanus toxoid in fresh and cryopreserved samples. Measuring cell proliferation with this dye has advantages over either 3H-thymidine or Bromodeoxyuridine (BrdU). Whereas the existing methods measure proliferation at a single time point, PKH26 gives a cumulative measure of cell proliferation. As PKH26 is incorporated into the cell membrane, cells do not have to be permeabilised to allow dye incorporation into a cytoplasmic compartment. Most importantly, PKH26 can be used in combination with monoclonal antibodies to surface markers on mixed populations of cells, to determine the proliferation of individual subpopulations, without the need for prior cell fractionation. We also show that PKH26 can be used with similar efficacy in both fresh and cryopreserved samples. In addition since PKH26 is a cumulative measure of proliferative responses we were able to show that restimulation of the dividing population in vitro with fresh antigen presenting cells (APC) and antigen permits characterisation of a further proliferating cell population. The use of PKH26 dye in combination with cell phenotyping and measurement of cytokine production at the single cell level will prove a powerful tool for multiparameter analyses of cellular responses to antigen.