Phenotyping of proliferating cells in cultures of human lymphocytes

Multiparametric flow cytometric analysis of the kinetics of surface molecule expression after polyclonal activation of human peripheral blood T lymphocytes

In this report we have analysed the kinetics of modulation of human peripheral blood T lymphocyte membrane molecules upon activation with optimal amounts of phytohaemagglutinin (PHA) and concanavalin A (ConA). The following activation-related and differentiation/adhesion molecules were selectively and concomitantly investigated on CD4+ and CD8+ subsets by dual colour flow cytometry: CD69, CD25 and CD71; CD2, CD45RA and L-selectin. Cultures were assayed after 24, 48, 72, 120 and 168 h of incubation with PHA and ConA. This approach allowed a comprehensive evaluation of membrane phenomena occurring during activation of normal resting human T lymphocytes. Data show that the kinetics of expression of these molecules follows a precise and consistent time-course with no major differences between CD4 and CD8 subsets. CD69 expression peaked at 24 h, whereas CD25 and CD71 expression peaked at 48/72 h with some differences between PHA and ConA activation. L-selectin expression started an evident decrease in step with culture time whose magnitude was dependent on the lectin used, being higher with PHA than with ConA. Conversely, the expression of CD45RA remained stable for 72 h and then briskly decreased with no major differences between PHA and ConA activation. CD2 molecules increased with time in number and density, although the percentage of positive cells remained essentially constant (greater than 85%). After 48/72 h of stimulation about 10% of cells co-expressed CD4 and CD8 molecules. To ascertain whether the phenomenon was restricted to cells in a particular activation state, the phenotype of cells in the diverse phases of the cell cycle was established. Results obtained show that only actively proliferating cells, that is cells in S and G2-M phases, co-expressed the two molecules, suggesting that such a phenomenon reflects a momentary dysregulation of the normal sequence of gene expression. The present data are also discussed in the light of the dynamic role of T lymphocyte activation and adhesion molecules in regulating cell-cell interactions, tissue localization and eventual immunological function.

Immunological marker analysis of mitogen-induced proliferating lymphocytes using BrdU incorporation or screening of metaphases. Staphylococcal protein A is a potent mitogen for CD4+ lymphocytes

The proliferative effects of the mitogens phytohaemagglutinin (PHA), concanavalin A (Con A), pokeweed mitogen (PWM), and staphylococcal protein A (SpA) were investigated using two different methods which enable immunological marker analysis of proliferating cells: either surface marker labelling followed by BrdU incorporation or screening of metaphases after surface marker labelling. Therefore peripheral blood mononuclear cells from six healthy volunteers were stimulated with these four mitogens. Both PHA and Con A gave rise to more CD8+ than CD4+ proliferating cells. PHA, but not Con A, induced B-cell proliferation as well. PWM mainly caused T-cell proliferation. SpA also appeared to be a potent T-cell mitogen in addition to its capacity to induce B-cell proliferation. However, in contrast to the other mitogens SpA predominantly stimulated CD4+ cells.

Detection of activated lymphocyte subsets by fluorescence and MTT staining

A double staining technique for simultaneously determinating cell surface phenotype and the degree of cell activation is described. As an activation marker, the tetrazolium dye MTT has been used. Cells were incubated for 30 min with MTT. Activated cells yielded a granular staining pattern. Upon termination of the reaction with sodium azide, a double-step immunofluorescence staining procedure using monoclonal antibodies specific for cell surface antigens was performed. The percentage of cells simultaneously displaying MTT formation and fluorescence was microscopically evaluated. Our results demonstrate that MTT staining is expressed concomitantly with the IL-2 receptor and the transferrin receptor. This method permits a simple characterization of activated T cell subsets and can be used clinically to analyse the T cell functions of patients being treated with immunosuppressive agents and patients with acquired immune deficiency syndrome.

Lymphocyte activation by phytohaemagglutinin and pokeweed mitogen. Identification of proliferating cells by monoclonal antibodies

Using a two-colour immunofluorescence technique, we have investigated the mitogenic effects of phytohaemagglutinin-M (PHA-M) and of pokeweed nitrogen (PWM) on human lymphocyte subsets. These were identified by CD1, CD3, CD4, CD8, and CD16 monoclonal antibodies, and proliferation was demonstrated by a polyclonal anti-transferrin antibody. Evidence has been obtained for the generation of a population expressing both the CD4 and CD8 antigens simultaneously, in short-term cultures of peripheral blood mononuclear cells in the presence of PWM and of PHA-M.

In vitro proliferation of lymphocytes from cyclophosphamide-pretreated mice immunized with antigen mixed with dimethyl dioctadecyl ammonium bromide

A blastogenesis assay employing lymphocytes from cyclophosphamide-pretreated mice immunized with antigen mixed with the immunopotentiating compound dimethyl dioctadecyl ammonium bromide is described. The model antigen used for determining the assay parameters was inactivated purified measles virus. The optimal time for removal of immunologically primed T cells was 7 days after immunization of mice pretreated 2 days previously with 200 mg of cyclophosphamide/kg. The peak lymphoproliferative response was found to occur after 3-5 days in culture, depending on the concentration of antigen used. Although fetal bovine serum and syngeneic mouse serum each worked well as a medium supplement, significantly higher specific and lower non-specific lymphoproliferation were obtained when the mouse serum was used. Most of the lymphocytes responding to antigen were of the Ly 1.2 phenotype. Specificity of the blastogenic response was shown by a lack of cross-reactivity among measles virus, herpes simplex virus type 1 and vesicular stomatitis virus antigens. This approach to a mouse blastogenesis assay involves an easy way to induce strong T cell priming in mice, while still providing an assay which has an ideal combination of low non-specific and high antigen-specific responses.

Reduced cellular immunity to varicella zoster virus during treatment for acute lymphoblastic leukemia of childhood: in vitro studies of possible mechanisms

To determine the effect of antileukemic therapy on preexisting immunity to varicella zoster virus, we studied 20 children with acute lymphoblastic leukemia maintained in complete continuous remission for greater than 1 year. Cellular immunity was tested by lymphocyte proliferation in response to varicella antigen. Antiviral antibody was measured using the fluorescent antibody to membrane antigen technique. Reduced lymphocyte proliferation was found in 9 of 16 seropositive patients when compared to an age-related control group. On the other hand, antibody titers in patients receiving chemotherapy remained positive and were essentially unchanged from pretreatment values. Shingles occurred in two of nine children with diminished and none of seven patients with normal cellular immunity, suggesting that proliferative responses to varicella antigen may have predicative value in identifying patients at risk for viral reactivation. Additional studies were done to determine if defective antigen presentation or reduced lymphocyte responder-cell frequency could account for the subnormal proliferative responses. Intact presentation of varicella antigens by patient mononuclear cells to parental, virus-specific T-cell blasts suggested that antigen processing was not defective. However, varicella-specific responder-cell frequencies measured by limiting dilution analysis were found to be depressed in most patients, including some with normal proliferative responses. Our findings indicate that therapy for acute lymphoblastic leukemia in children can be associated with depressed cell-mediated immunity to varicella zoster virus even though patients remain seropositive. Further studies suggest that while monocyte-mediated antigen presentation remains intact, virus-specific lymphocyte numbers decline and probably contribute to decreased cellular immunity to varicella zoster virus in children being treated for leukemia.