Human lymphocyte transformation induced by mitogens and antigens in a serum-free tissue culture system

Culture and Stimulation of Tammar Wallaby Lymphocytes

We describe the culture and stimulation of lymphocytes from the model marsupial, the tammar wallaby (Macropus eugenii). We also describe the capacity of tammar wallaby lymphocytes isolated from blood, spleen and lymph nodes to produce soluble immunomodulatory factors. Culture conditions were optimized for mitogen-driven stimulation using the plant lectin phytohaemagglutinin (PHA). Products secreted by stimulated cells were harvested and crudely fractionated before they were added back to freshly isolated lymphocytes. Using the 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) assay, both stimulatory and inhibitory bioactive factors were detected in serum-free supernatants harvested from mitogen-treated peripheral blood mononuclear cells. This paper describes the capacity of leukocytes of the tammar wallaby to respond to mitogenic stimulation and to produce soluble, low-molecular-weight bioactive molecules that possess cytokine-like activity.

In vitro proliferative response of human peripheral blood mononuclear cells to concanavalin A

The proliferation response of human peripheral blood mononuclear cells (PBMC) to concanavalin A (con A) was tested in a medium with or without addition of fetal calf serum (FCS) or a serum substitute. The time profile of the proliferative response of PBMC to con A was different in cells cultured in a medium supplemented with or without FCS. This different pattern occurred for the con A-induced DNA-synthesis as well as for the RNA- or protein-synthesis. The peak proliferation rate and the stimulation index of proliferation of human PBMC to con A was also higher when the cells were cultured in a medium with 10% FCS compared to cells cultured in a FCS-free medium. Substitution of the fetal calf serum by a serum substitute even induced a profound inhibition of the de novo synthesis of DNA in human PBMC. The results indicate that a lymphocyte proliferation response to con A can still be obtained in a culture medium where no FCS was added, although a weaker stimulation occurred in comparison to a culture medium with FCS. However, addition of a serum substitute caused a marked inhibition of the lymphocyte proliferation rate.

A serum-free medium for human primary T lymphocyte culture

This paper describes a defined serum-free medium (SFM), designated A-X, which supports in vitro proliferation of human primary T cells stimulated with mitogens, two-way mixed leukocyte reactions, anti-CD3, and a superantigen. A-X is a 1:1 mixture of two commercially available SFM, AIM V and EX-CELL 300. In each assay tested it supported uptake of [3H]thymidine as well as or better than the standard culture medium, namely RPMI 1640 supplemented with 10% fetal calf serum. A-X also allowed the detection of interleukin-2 by ELISA at levels comparable to those produced in serum-supplemented medium. A-X will likely be useful in further studies as it eliminates many of the problems usually associated with the use of serum-supplemented media.

Mitogen-induced lymphocyte transformation in four different serum-free media

The proliferative responses of lymphocytes induced by the mitogens phytohemagglutinin (PHA), pokeweed mitogen (PWM) and concanavalin A (ConA) were tested in four different serum-free lymphocyte culture media in which serum was replaced by commercially produced serum substitutes. Two of the serum-free lymphocytes cultures (SF-X and FEB-100) achieved proliferative responses to PHA and PWM comparable with those obtained in medium containing fetal calf serum, but only when the cell number was increased, whereas none of the lymphocyte cultures in serum-free medium showed adequate proliferative responses to ConA stimulation. The essential factors in serum-free media for optimal growth and mitogen stimulation of lymphocytes include insulin, transferrin, electrolytes, glutamine and a high cell concentration.

Accessory cell requirements in mitogen-induced rabbit T lymphocyte proliferation in an improved tissue culture system

The impact of an improved culture medium (IMDM+), consisting of Iscove's modified Dulbecco's medium supplemented with albumin, transferrin, insulin, zinc, 2-mercapthoethanel, and 0.1% fetal bovine serum was investigated in phytohemagglutinin (PHA)-induced rabbit T cell proliferation. At the number of 2 X 10(5) cells/well purified T lymphocytes cultured in IMDM+ responded 3 to 10 times better than lymphocytes cultured in serum-supplemented RPMI 1640 medium. In these conditions, PHA-induced proliferation seemed not to require the presence of accessory cells. However, at lower cell numbers, T cell proliferation was more efficient when calculated on a per cell basis. At these low cell numbers, optimal proliferation required accessory cells like macrophages or dendritic cells. The apparent absence of this requirement for accessory cells at high T cell concentrations may be explained by the contribution of contaminating macrophages and dendritic cells in the purified T cell fractions.

A new method to detect directly in culture cell surface membrane immunoglobulins

An ELISA assay is described for the measurement of the smIgG. The method is based on the detection of cell-smIgG directly on the same microplate used for the culture. The cells, preincubated at 37 degrees C for one hour, were cultured in the presence of S-ConA and serum-free medium for two days. Using this strategy, the background noise due to non specific adsorption of IgG to plastic wells and cytophilic antibodies was eliminated. The cells in the presence of S-ConA and serum-free medium adhered to the plastic wells, and the cell-smIgG were detected using an anti-human IgG covalently linked to alkaline phosphatase or its F(ab')2 fragment. The possibility of measuring the modulation of the expression of the cell-smIgG without any additional manipulation is stressed.

Immunosuppressive effect of early pregnancy factor on early expression of cell surface membrane IgG

We have adopted a new assay to investigate the influence of early pregnancy factor (EPF) on the modulation of lymphocyte activity. Lymphocytes were attached to the plastic surfaces of microplates in serum-free medium in the presence of Sepharose-Con A. After 2-3 days incubation with EPF, and ELISA assay was used to detect the expression of surface membrane IgG (smIgG); this was done in the same microplates used for the culture, thus avoiding cell manipulation. Using only a few picograms of EPF a significant inhibition (in the range 26-40%) was obtained. The variation in the inhibition observed was mainly due to the different sources of lymphocytes used. Unrelated proteins and hormones, tested at the same concentration as EPF, did not show any inhibitory activity. Using the F(ab)2 fragment of anti-human IgG instead of the whole molecule the same levels of inhibition were obtained, suggesting that the observed inhibition by EPF was not due to a non-specific interaction between the anti-human IgG and the Fc receptors on the cell. Such inhibitory activity detected in vitro by this method provides additional support for a suppressive role for EPF during pregnancy.

Development of a chemically defined serum- and protein-free medium for growth of human peripheral lymphocytes

A chemically defined, protein-free medium (designated CFBI 1000, where CFBI = Clayton Foundation Biochemical Institute) that supports human peripheral lymphocyte proliferation has been developed. This medium allows exploration of individual metabolic differences by varying the medium composition as well as providing a base to explore further the mechanisms of lymphocyte activation in a system initially free of added macromolecular species other than mitogen. The peripheral blood lymphocyte is an ideal system for metabolic studies because it is easily obtained, is a primary resting cell that can be activated to proliferate, and presumably reflects both the genetic makeup and biochemical environmental history of the individual at the time the cells were formed. Examination of the role of various factors in lymphocyte activation and subsequent events may be simplified by the utilization of a medium that is protein-free and chemically defined. The CFBI 1000 medium supports the growth response of human peripheral lymphocytes to mitogen as measured by [3H]thymidine incorporation to an extent comparable to other media used widely in assessment of lymphocyte proliferation.

Human secondary immune responses induced by influenza in a serum-free tissue culture system

Peripheral blood lymphocytes are capable of producing antibody in response to antigenic stimulation by a recall antigen, influenza, during culture for 10 days in medium consisting of 1 part Ham's F-12 and 1 part Iscove's modified Dulbecco's medium supplemented with sodium bicarbonate, bovine crystalline insulin, human transferrin, 2-mercaptoethanol, progesterone, and bovine serum albumin. Anti-influenza antibody levels in the supernatants were determined by enzyme-linked immunosorbent assay. Optimal conditions for production of anti-influenza antibody in this serum-free medium were: influenza concentration, 0.032-0.125 HAU/ml; day of harvest, 10; and cell concentration, 3.0-4.0 X 10(5) cells in 200 microliter of medium per well. Use of serum-free medium will allow examination of the effects of various additives to tissue culture without concern for unknown factors or potential interaction with serum.

Early protein synthesis in activated human peripheral blood mononuclear cells

Though B-cell division and Ig synthesis in response to pokeweed mitogen (PWM) require interaction with T-cells and monocytes, it is not clear which earlier events in B-cell activation share this requirement, and which are the result of direct interaction of mitogen with the B-cell. Having previously shown that the acceleration of lecithin synthesis in human B-cells at 16-20 hr requires both T-cells and monocytes, we now examine whether B-cells require similar interactions to increase their protein synthetic rate, another important activation event. At 21-24 hr of PWM stimulation, the stimulation index (SI) for incorporation of [35S]methionine into protein was 2.1 +/- 0.4 for unfractionated cells, 1.7 +/- 0.1 for B-cells, 2.5 +/- 0.1 for T-cells, and 3.4 +/- 0.5 for monocytes. Thus monocytes contributed substantially to early mitogen-induced protein synthesis by human peripheral blood mononuclear cells. When the monocyte/B-cell fraction (MB) and T-cell fraction (T) were mixed at various ratios in PWM-stimulated cultures, synergy was apparent at MB:T ratios of 1:1 and 1:2, indicating cell interactions augmented early mitogen-driven protein synthesis in at least one of these cell types. However, much or all of this synergy could be attributed to T-cells, whose protein synthetic response was augmented by B-cells and monocytes. In contrast, the early increase in B-cell protein synthesis appeared to be independent of cell interactions, since their SI of 1.7 was not influenced by varying the proportion of M- or T-cells over a 50-fold range. These contrasting results between two contemporary events fits the hypothesis that one (accelerated phospholipid synthesis) requires a first signal plus one or more cell interaction signals, whereas the other (accelerated protein synthesis) requires only the first signal.

Serum-free medium for generation and propagation of functional human cytotoxic and helper T cell clones

A serum-free lymphocyte culture medium is described in which serum is replaced by bovine serum albumin, transferrin, insulin, ethanolamine and a mixture of saturated and unsaturated fatty acids (linoleic acid, oleic acid and palmitic acid). In this serum-free medium proliferative and cytotoxic responses induced in mixed lymphocyte culture were comparable with those obtained in medium containing serum. Antigen-specific cytotoxic and helper T cells were isolated and could be propagated in serum-free medium without loss of function.

Termination of tritiated thymidine incorporation by freezing the cells

It is often desirable to be able to stop the uptake of tritiated thymidine by a number of transforming lymphocyte cultures at a specific time. This is important for kinetic studies but may be difficult if the number of cultures to be harvested at one time is large. We describe in this report a simple method to stop the incorporation of tritiated thymidine into any number of transforming lymphocyte cultures simultaneously.

Lymphokine production and lymphocyte transformation by human mononuclear cells in a serum-free medium

In order to study the effects of purified serum proteins, such as complement components, on human lymphoid cell functions, we have developed a serum-free culture medium that supports lymphocyte transformation and lymphokine production. The medium is comprised of RPMI 1640 containing commercially available purified human serum albumin (HSA). Optimal proliferative responses to mitogens and antigens were noted at HSA concentrations of 2.5-10.0 mg/ml, and at a cell density of 1 X 10(6) mononuclear cells/ml. In medium supplemented with 5 mg/ml HSA, it was found that lymphocyte transformation responses, release of interleukin 2 and leukocyte inhibition factor (LIF), and the one-way mixed lymphocyte reaction proceeded in a manner analogous to that in plasma-supplemented cultures. Stimulation of LIF release by C3b was seen in HSA-supplemented cultures but not in serum-free conditions or in cultures containing 12% autologous plasma. This system can thus be used to examine cell-mediated immune responses without the interference of plasma proteins other than HSA.

Induction of immunoglobulin-producing human peripheral blood lymphocytes in serum-free medium

Induction of immunoglobulin-secreting cells from human peripheral blood lymphocytes in a serum-free culture medium was studied. Albumin, transferrin, insulin and fibronectin can replace serum entirely for support of pokeweed mitogen (PWM)-stimulated B lymphocytes, measured by a reverse hemolytic plaque assay using protein A-coated red cells. In this serum-free system, growth and maturation to IgM and IgG secretion occur at the same or higher efficiency as in conventional serum-containing medium, with maximum numbers of plaque-forming cells on day 6 at optimal dose of PWM, 0.5-5 micrograms/ml. This system can be used to avoid the interference from undefined serum components.