PubMed Health⌕ Search

Biomedical subjects

G Ramila

Publications and source records attributed to G Ramila.

6 recordsLinked to original sources
PubMed1985

Evaluation of accessory cell heterogeneity. I. Differential accessory cell requirement for T helper cell activation and for T-B cooperation.

Several Ia+ tumor cell lines and peritoneal exudate macrophages were tested as accessory cells (AC) for the activation of antigen-specific T cells and for T-B cooperation. The macrophages and all the Ia+ tumor lines tested induced the release of lymphokines from T cells in a major histocompatibility complex (MHC)-restricted fashion and reconstituted the antibody responses of AC-depleted spleen cells or of purified T and B cells. However, only the normal macrophages but none of the tumor lines induced carrier-specific T helper (Th) cells which help B cells for specific antihapten antibody responses by linked recognition. For T-B cooperation accessory cells were also required, but in contrast to Th cell activation any type of Ia+ AC (e.g. macrophage or tumor line) was effective. Strong MHC-restriction between the lymphocytes and the AC was seen if antigen-pulsed AC were added into the AC-depleted T-B cooperation cultures. If the AC and antigen were concomitantly added to the AC-depleted T-B cultures, MHC-restriction was less obvious. Concanavalin A supernatant reconstituted the response of AC-depleted T-B cultures provided antigen-specific Th cells and the hapten-carrier conjugate were present. If, however, tumor line-activated T cells were added instead of macrophage-induced Th cells, no cooperation with B cells took place even in the presence of Con A supernatant. The results obtained demonstrate a differential AC requirement for the induction of Th cells depending on the differentiation stage of the Th cells.

Animals↗
PubMed1985

Evaluation of accessory cell heterogeneity. II. Failure of dendritic cells to activate antigen-specific T helper cells to soluble antigens.

The activation of antigen-specific T cells requires Ia+, antigen-presenting accessory cells (AC). Dendritic cells (DC) and macrophages (M phi) isolated from spleen an peritoneal exudate were tested as AC for the activation of the activation of T helper cells and the induction of T cell proliferation. The cell separations to obtain DC and splenic M phi were performed by discontinuous bovine serum albumin gradients, adherence on petri dishes and rosetting with opsonized sheep erythrocytes. DC as well as the M phi were able to induce antigen-specific T cell proliferation, but only the M phi and not the DC activated antigen-specific T helper cells which help B cells for antibody production to soluble antigens. Keyhole limpet hemocyanin-specific T cells repeatedly stimulated with DC and antigen also did not express helper activity. The failure of DC to induce T helper cells was not due to the activation of a suppressor pathway. Thus, dendritic cells, although very efficient as AC in the induction of various T cell functions, are not able to activate T helper cells required for carrier-specific T-B cooperation and therefore cannot be the sole accessory cells. Based on these results and on previous data using Ia+ tumor cell lines as AC, we confirm the existence of functional AC heterogeneity.

Animals↗
PubMed1985

Evaluation of accessory cell heterogeneity. III. Role of dendritic cells in the in vitro activation of the antibody response to soluble antigens.

Dendritic cells and macrophages obtained from spleen and peritoneal exudate were tested as accessory cells for the activation of lymphokine production by T cells, for supporting T-B cooperation and for the induction of antigen-specific T helper cells. Dendritic cells as well as macrophages were able to activate T cells for interleukin-2 secretion and functioned as accessory cells in T-B cooperation, but only macrophages induced T helper cells, which cooperate with B cells by a linked recognition interaction, to soluble antigens. Dendritic cell- and antigen-activated T cells also did not help B cells in the presence of Con A supernatants which contained various T cell- and B cell-stimulatory factors. The failure of dendritic cells to differentiate memory into functional T helper cells, but their efficient accessory cell function in T-B cooperation, where functional T helper cells are already present, can be best explained by a differential accessory cell requirement for T helper cell activation dependent on the differentiation stage of the T helper cell.

Animals↗
PubMed1983

Evaluation of Ia+ tumor cell lines and peritoneal exudate macrophages as accessory cells: differential requirements for the activation of certain T cell functions.

Several Ia+ (BC3A, TA3, D1B) or Ia-inducible (WEHI-3, P388D1) tumor lines were tested for accessory cell function for the activation of antigen-specific T cell proliferation and for the induction of T helper cells that help B cells in antibody production. All lines were able to induce antigen-specific T cell proliferation in an MHC-restricted way, but none activated T helper cells to soluble antigens under all conditions tested. In comparison, starch-induced peritoneal exudate macrophages induced T cell proliferation as well as T cell help. Some of the lines tested induced nonspecific suppressor cells that were Ly-2-positive and partially or completely inhibited antibody responses. The induction of suppressor cells, however, is not the reason for the failure of the tumor lines to activate T helper cells. These data indicate that antigen-specific T cell proliferation and helper activity do not necessarily correlate.

Animals↗
PubMedDate not supplied

Accessory cell-dependent selection of specific T-cell functions.

Activation of many T-cell functions depends on their interaction with antigen-presenting accessory cells which express I region associated (Ia) products. Cells expressing accessory cell function include those of the monocyte/macrophage lineage and dendritic cells. More recently, B cells and a number of tumour cell lines of macrophage or B-cell origin were shown to act as accessory cells in certain assays. We showed previously that normal peritoneal exudate macrophages (PEC) induced both T-cell proliferation as well as T-cell help, whereas various Ia+ tumour lines of macrophage or B-cell origin, although stimulating antigen-specific T-cell proliferation, did not significantly activate T-cell help. We report here that during the initial T-cell activation in vitro accessory cells (PEC or Ia+ tumour cells) select particular T cells to express previously determined functions. Moreover, some tumour cell lines induce suppressor T cells which inhibit helper activity.

Animals↗