Cryopreservation enhances interleukin-1 production in human mononuclear cells

Cryopreservation of peripheral blood mononuclear cells does not significantly affect the levels of spontaneous apoptosis after 24-h culture

Studies performed with malaria patients living in endemic areas are frequently conducted in laboratories located hundreds of kilometer away from research centers, due to the difficulties in performing the assays in field conditions. Thus, we considered the potential indication of cryopreservation of peripheral blood mononuclear cells (PBMC), in most fieldwork, and decided to evaluate the effect of cryopreservation of PBMC on spontaneous apoptosis. The membrane integrity of PBMC was tested using three previously described protocols of cryopreservation. Cell samples were obtained from 19 healthy volunteers. Percentage of apoptotic nuclei in short-term PBMC cultures was determined by a sensitive method using 7-aminoactinomycin D followed by flow cytometry. Our results indicate that although cryopreservation can to some extent affect lymphocyte membrane integrity rates, flow cytometry analysis showed that frequencies of spontaneous apoptosis in cryopreserved cells were not significantly modified after 24-h culture. It is concluded that cryopreserved PBMC could be used for measuring spontaneous apoptosis and therefore, could be employed for the study of populations living in areas distant from research centers, allowing the comparative evaluation of samples obtained at different time.

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

In view of the wide usage of frozen PBMCs as stem cell support following high-dose chemo- and/or radiotherapy, and the pleiotropic activities of tumor necrosis factor-alpha (TNF-alpha), the influences of freezing and radiation on LPS-induced TNF-alpha production by human peripheral blood mononuclear cells (PBMCs) were studied. Frozen PBMCs secreted significantly larger quantities of TNF-alpha than fresh cells. Blocking of endogenous IL-10 by neutralization with anti-IL-10 monoclonal antibody resulted in further augmented and prolonged secretion of TNF-alpha by both the fresh and frozen cells. In contrast, addition of exogenous IL-10 to LPS-stimulated cultures inhibited TNF-alpha secretion. In vitro irradiation had an inconsistent effect on TNF-alpha production by the fresh PBMCs. Taken together, these results suggest that the endogenously hypersecreted TNF-alpha is indirectly responsible for the previously reported elevated IL-1-, IL-6-, and IL-10-secreting capabilities of frozen PBMCs. They also indicate that the TNF-alpha induced IL-10 and then down-regulates the monocytes from further TNF-alpha secretion. Considering the vital role played by TNF-alpha in antimicrobial and antitumor activities, in the immune system, and in the pathogenesis of many acute and chronic diseases, the abilities of frozen cells to produce large quantities of TNF-alpha in response to infectious agents could have profound impact on patients receiving such frozen PBMCs as stem cell support following myeloablative therapies.

Effects of cryopreservation on immune responses: IX. Stimulus-mediated dichotomy in IL-10 production by frozen human peripheral blood mononuclear cells

The effects of freezing on phytohemagglutinin (PHA) and lipopolysaccharide (LPS)-induced interleukin-10 (IL-10) production by human peripheral blood mononuclear cells (PBMC) were studied. The freezing process had a divergent effect on the production of IL-10 by PBMC. Frozen PBMC produced significantly smaller amounts of IL-10 in response to PHA stimulation while secreting significantly larger quantities in response to LPS activation. In vitro irradiated PBMC produced significantly smaller amounts of IL-10 in response to both PHA and LPS stimulation. The results indicate that the functional inactivation of a naturally occurring subset of cryosensitive and radiosensitive immunodownregulatory cells is responsible for the observed divergence. They further suggest that, in addition to other mechanisms, a reduction in the secretion of this cytokine synthesis inhibitory factor by the frozen PHA-activated cells could have contributed to the previously reported, augmented IL-2 and IFN-gamma-secreting capabilities of frozen PBMC. The significance of this freezing-induced deviation in IL-10 secretion by PBMC in relation to cancer therapy is discussed.

Procoagulant and profibrinolytic activities of cryopreserved human monocytes

The purpose of this study was to compare the ability of fresh and cryopreserved mononuclear cells to generate thrombin, induce fibrin formation and finally resolve the fibrin formed, when exposed to plasma. Peripheral blood mononuclear cells (PBM) from 4 donors were collected by gradient centrifugation on Lymfoprep, and cryopreserved in fetal calf serum and 10% dimethyl sulfoxide. Viability was tested by exclusion of trypan blue, as well as green/red fluorescence of fluorescein-diacetate and ethidium bromide (FDA/EB). Fresh and frozen-thawed cells were seeded, stimulated with lipopolysaccharide(LPS), and exposed to a standard heparinized overlay plasma. Plasma was harvested at intervals (0-7 days). Thrombin generation and fibrin formation were measured by quantification of prothrombin fragment (F1 + 2) and fibrinopeptide A (FPA) and the fibrinolytic capacity of the cells as the amount of fibrin (ogen) degradation products (FbDP and FgDP). Recovery of cells after thawing was about 80%, and the viability of fresh and cryopreserved PBM was > 95%. Compared to fresh, frozen cells fully retained their capability of Tissue Factor synthesis, leading to prothombinase activity (F1 + 2) and fibrin formation (FPA). In contrast, the fibrinolytic capacity of frozen-thawed cells were significantly reduced. As expected there were significant variations between the donors in all the parameters measured. We conclude that cryopreservation of human blood mononuclear cells is possible with maintainance of the potential of the cells to mediate coagulation in plasma upon LPS stimulation, whereas the fibrin resolving capacity apparently is reduced by the preservation procedure.

Cryopreservation-induced enhancement of interleukin-2 production in human peripheral blood mononuclear cells

To better understand the effects of cryopreservation on various immunocompetent cell functions, we have examined the interleukin-2 (IL-2)-producing activities of frozen mononuclear cells (MNCs) from healthy subjects. The mechanisms responsible for the observed effects were also analyzed. Both the unfractionated and monocyte-depleted, frozen MNCs produced significantly larger quantities of IL-2 than fresh cells. Similar to freezing, L-leucine methyl ester (Leu-OMe) treatment (to eliminate IL-1 and prostaglandin E-2 (PGE-2)-secreting cells) also increased the IL-2-producing activities of fresh cells, but freezing no longer enhanced the production of IL-2 by Leu-OMe-treated cells, suggesting that (1) both the freezing process and Leu-OMe treatment have similar effects on IL-2 production, (2) the increased IL-2 secretion by frozen MNCs is independent of IL-1, and (3) inactivation of PGE-2-secreting cells during the freezing procedure is responsible for increased IL-2 secretion. Elimination of CD8+ T cells (putative suppressor cells) from MNCs has also resulted in the production of increased amounts of IL-2 by fresh cells, and again, freezing did not further enhance the IL-2-secreting activities of MNCs, that are devoid of CD8+ T cells. This confirms that the increased IL-2 production is due to the inactivation of immuno-down-regulatory cells. The results provide further evidence that the lack of active, suppressor T cells, monocytes, and increased IL-1 and -2 production may be responsible for the previously reported enhanced immunoglobulin-producing abilities of cryopreserved cells from healthy subjects and from patients with lung cancer.