Morphological study of autologous rosettes (A-RFC)

Role of autorosette forming cells in antibody synthesis in vitro: suppressive activity of ARFC in humoral immune response

The role of autologous rosette forming cells (ARFC) in humoral immune responses was studied using an in vitro system. While depletion of ARFCs from PBL resulted in a significant increase of either total IgG or anti-TT IgG, addition of these cells to the system decreased the production of immunoglobulin to a level comparable to that of unfractionated PBL. The majority of the ARFCs reacted with anti-Leu2a and anti-Leu8. In contrast, the majority of non-ARFCs reacted with Leu3a and only 10% with Leu8 monoclonal antibodies. Stimulation of unfractionated PBL with concanavalin A (ConA) resulted in an increase of the ARFC population. ConA stimulation also increased the number of cells reactive with anti-Leu2 and/or anti-Leu8. The autorosette population had a higher purine nucleoside phosphorylase (PNP) content than the non-ARFC population. Although the ARFC suppressed synthesis of antibody by B cell in vitro when they were mixed with either autologous or allogeneic B cells, a marked proliferation of non-B cells was evident. We conclude that at least two different subpopulations of T cells are capable of forming rosettes with autologous red blood cells.

Studies on mouse auto-reactive cells. II. Cytotoxicity exerted by mouse lymphocytes against syngeneic erythrocytes

In mice, an in vitro cell-mediated cytotoxicity is directed towards syngeneic erythrocytes used as targets. This phenomenon occurs in lymphoid organs of normal, non-immunized mice. Its intensity is greater in the thymus than in spleen or lymph nodes. The study of the nature of the cell responsible for this spontaneous syngeneic cytotoxicity ruled out the role of macrophages. The involvement of T cells in this phenomenon is assessed by its disappearance after the lymphoid cells had been treated with anti-theta serum plus complement, by its disappearance from lymphoid organs of mice previously treated by hydrocortisone, and by its decrease in the presence of synthetic thymic factor. Moreover, spontaneous syngeneic cytotoxicity is lost when lymphoid cells are depleted at autologous rosettes by centrifugation on a Ficoll-Hypaque gradient after rosette formation. Cytotoxic lymphocytes might belong to the population of auto-rosettes previously characterized as a population of immature T cells.

[Living Sézary cells in vitro: formation of autologous rosettes (author's transl)]

Living Sézary cells are more clearly discernible in supravital preparations using a phase contrast microscope than in stained blood smears. Especially, the small variant of the Sézary cell can easily be identified by this simple technique. Lymphoblasts are unequivocally discernible from monocytes, since functional criteria of the living cells can be evaluated in supravital preparations in addition to morphological characteristics. Using this technique a remarkable phenomenon was seen in living Sézary cells: interactions between autologous erythrocytes and the atypical lymphocytes created autologous rosettes. The binding of erythrocytes with a typical lymphocytes was so stable that even with good motility of the Sézary cells the erythrocytes adhered to the surface of the lymphocytes. The ability of living Sézary cells to build rosettes with autologous erythrocytes in vitro is taken as an indication that living Sézary cells have membrane markers of thymocytes.

Macrophage factors that enhance the antibody response

The immunological mechanism of the primary in vitro antibody responses to sheep erythrocyte antigens involves soluble immunomodulatory factors. These studies have demonstrated that the stimulation of immunocytes with lipopolysaccharide (LPS) induced the release of a helper factor which appeared to be a monokine. This helper factor was released by stimulated adherent splenocyte cultures but not by nonadherent cell populations. The P388D-transformed macrophage cell line also produced the factor in response to LPS. LPS-induced helper factors were absorbed from solution by bone marrow cells but not by thymocytes, thereby indicating that the factor may selectively bind to B-cells or to undifferentiated stem cells. Mature T-cells did not appear to be involved in the immunostimulatory effects of this macrophage-derived factor as evidenced by the results of several studies. These included observations that splenocytes from athymic BALB/c nu nu mice both produced the factor and responded to it.