Effects of purified measles virus components on proliferating human lymphocytes

Early signal transduction in measles virus-infected lymphocytes is unaltered, but second messengers activate virus replication

In order to understand measles virus-lymphocyte interactions, we have started to analyze factors and events which regulate measles virus infection in peripheral blood mononuclear cells (PBMC). We analyzed the initiation of cell proliferation, induced by phytohemagglutinin, in infected and control PBMC by measuring intracellular free Ca2+ by using fura-2. Measles virus-infected and control PBMC responded similarly with an increase in the amount of cytosolic free Ca2+, indicating that the early activation events are not affected and are not involved in immunosuppression. The activation signals, Ca2+ and protein kinase C, induced specifically and independently by Ca ionophore A23187 or 12-O-tetradecanoylphorbol-13-acetate (TPA), changed the restricted measles virus infection to a productive one. The combination of TPA and A23187 was the most potent activator of measles virus replication. TPA and A23187 operate through different activation mechanisms, and it is evident that measles virus replication depends on the activation of cellular signal pathways. Depletion of adherent cells enhanced virus replication, especially at the early stage of infection, indicating the inhibitory role of monocytes. Monocytes were strongly infected, but they supported complete measles virus replication only at a very low level, and virus replication could not be enhanced with TPA and/or A23187.

T-lymphocyte subpopulations in relation to immunosuppression in measles and varicella

Patients with measles or varicella were studied during the acute phase (first week) of illness and, after recovery, by lymphocyte stimulation tests and determination of T-lymphocyte subpopulations, using the monoclonal antibodies Leu 2a and Leu 3a directed at the suppressor/cytotoxic and the helper T-cell subsets, respectively. Low proliferative responses to phytohemagglutinin were found during the acute phase of both diseases. The response to purified protein derivate of tuberculin was also low in all measles patients tested and in some of the varicella patients. In both infections increased spontaneous DNA synthesis was demonstrated. In the acute phase of measles there was T lymphocytopenia but no change of the ratio between T lymphocytes of helper and suppressor/cytotoxic cell phenotypes. In the acute phase of varicella the percentage and the absolute number of Leu 2-positive (suppressor/cytotoxic) T cells were increased. Measurement of the size of the lymphocytes indicated activation of this subset. Cryopreserved blood mononuclear cells from the acute phase of varicella could suppress the phytohemagglutinin response of autologous convalescent-phase cells. This was not seen when cells from measles patients were tested. The suppression of the lymphocyte stimulation response in varicella is probably in part caused by activation of suppressor cells, whereas the suppression of the stimulation response in measles seems to be due mainly to other mechanisms.

Replication of poliovirus and measles virus in cultures of human lymphoblastoid and of Burkitt lymphoma cell lines

Poliovirus type 1 replicated in 4 different human lymphoblastoid cell lines (LBL) transformed in vitro by EBV virus or isolated from cases of mononucleosis. Maximum virus titers were reached 2--4 days after inoculation. There was a decrease in percentage of viable cells in the infected cultures but a considerable fraction of cells was not destroyed by virus replication. A persistent low grade replication of virus was observed and demonstrable during 56 days after inoculation in one LBL cell line. Presumably a small fraction of cells supporting virus replication is continuously recruited from refractory cells. No virus propagation was demonstrable in 4 Burkitt lymphoma (BL) cell lines. Measles virus grew efficiently in both types of cell lines. Using indirect immunofluorescent technique poliovirus and measles virus antigen could be demonstrated in the cytoplasm of LBL cells in parallel with disappearance of F-actin containing microvilli.

Lymphocyte blast transformation responses and viral antibodies in relation to HLA antigens in multiple sclerosis

Fifty four clinically stable multiple sclerosis (MS) patients and 54 age- and sex-matched control subjects were HLA-typed, and their responses to herpes simplex, measles, mumps and rubella antigens were examined by the lymphocyte blast transformation test and by serum antibody titrations. Blast transformation response to purified tuberculin (PPD), mitogen phytohaemagglutinin (PHA), pokeweed mitogen (PWN) and concanavalin A (Con A) and spontaneous proliferation of lymphocytes were also studied. MS patients differed from controls by higher antibody levels to measles and rubella viruses and by lower specific blast transformation responses to rubella and measles antigens. When the relative strength of transformation responses was measured, mumps and herpes simplex responses were also lower in MS patients than in controls. In addition, spontaneous lymphocyte proliferation of MS patients in 6-day cultures was lower than that of control lymphocytes. In mitogen stimulations there were no differences between whole groups, but the oldest patients had lower responses to PHA and Con A than their matched controls. The frequency of HLA-Dw2 was 56.6% in MS patients and 32.1% in controls. The patients with and without Dw2 differed from each other only by a lower specific response to PPD in the Dw2-positive group. The immunological response of Dw2-positive controls resembled that of MS patients: low transformation response to viral antigens, low spontaneous proliferation and elevated measles antibodies. This finding supports the function of a genetically determined type of immune responsiveness with low cell-mediated immunity and high levels of certain viral antibodies as one susceptibility factor in multiple sclerosis.

Lymphocyte blast transformation responses in measles infection

Lymphocyte blast transformation responses were studied in eight patients with natural measles infection. A specific response to purified measles virus antigen and a weaker response to crude measles virus antigen were found after infection. The response to purified measles antigen appeared 1-3 weeks after the beginning of the rash, when the great number of proliferating mononuclear cells found in the peripheral blood during the rash was declining. In the first weeks after onset of the rash also leucocyte and lymphocyte numbers were decreased, and specific responses to purified tuberculin (PPD) and to rubella and mumps virus antigens were suppressed. In mitogen stimulation tests there was no significant suppression of phytohaemagglutinin and concanavalin responses in this small series, but the response to pokeweed mitogen was decreased. The responses to antigens other than measles virus antigens recovered in parallel with the increase of the measles-specific response.