Peter M. Lydyard

CD5 mRNA Expression and Auto‐Antibody Production in Early Human B Cells Immortalized by EBV

A number of studies have suggested that lymphocytes producing polyreactive antibodies belong to the CD5+ B‐cell subset. In this study we have examined CD5 at the cell surface and mRNA levels in EBV‐driven cord blood and fetal liver clones previously characterized in terms of their antibody specificities. We show that EBV‐immortalized cells can express surface CD5, and that some of the clones not expressing surface CD5 express it at the mRNA level. The complete absence of CD5 mRNA in some polyreactive clones is consistent with the proposition that the production of auto‐antibodies and multispecific antibodies is not restricted to the CD5+ B‐cell subset.

Receptors for IgM are expressed on acute lymphoblastic leukemic cells having T-cell characteristics

Abstract Six acute lymphoblastic leukemia (ALL) patients were studied whose lymphoblasts formed rosettes with sheep erythrocytes to determine if they expressed a receptor for IgM, which is a characteristics of normal T cells; chronic lymphocytic leukemia (CLL) cases carrying B-cell markers were compared as controls. In all six cases of ALL, but not CLL, IgM was expressed after overnight incubation in tissue culture medium. It is therefore considered that the IgM receptor can be used as an additional reliable marker for classifying leukemic disorders.

ANALYSIS OF SURFACE PROPERTIES, FINE STRUCTURE AND ORGAN DISTRIBUTION OF TWO DISTINCT T-CELL SUBPOPULATIONS: Tμ AND Tγ

Publisher Summary This chapter discusses surface properties, fine structure, and organ distribution of two distinct T-cell subpopulations, Tμ and Tγ. Cytocentrifuged Tμ cells stained with Giemsa show the characteristics of small lymphocytes with dense accumulations of nuclear chromatin and a thin rim of basophilic cytoplasm. On the contrary, Tγ lymphocytes appear as larger cells with a homogeneously stained nucleus and a much wider rim of weakly basophilic cytoplasm containing vacuoles and granules. Size, number, and distribution of these cytoplasmic granules vary from cell to cell; they are strongly acidophilic, and in preliminary experiments described in the chapter, they did not stain with either the periodic acid–Schiff reaction or with Alcian blue at pH 2.5. This suggests that they do not contain glycoproteins. Viewed under the electron microscope, Tμ lymphocytes have a smooth surface and poorly represented cytoplasmic organelles. Tγ cells have a rough surface, with many long microvilli; the cytoplasm is rich in mitochondria, single ribosomes, and scattered strands of rough endoplasmic reticulum. The Golgi apparatus is also well developed in piles of tubules and cisternae, and the granules are formed of a dense matrix surrounded by a membrane unit; these are found in close proximity to the Golgi apparatus and sometimes near the plasma membrane.

Unique Aspects of Immunoglobulin Expression During Early B Cell Differentiation in the Chicken

Perhaps the most significant events during the life history of B cells are changes in the expression of immunoglobulin genes. In this regard, results of studies in birds and mammals suggest that B cell development can be conveniently divided into 3 principle stages. The first is primarily concerned with the generation of clonal diversity; during this stage, non-Ig producing stem cells differentiate and divide to form large numbers of B lymphocytes, each expressing IgM antibodies of a single specificity. Next, the generation of isotype diversity occurs within B cell clones; limited numbers of cells within each clone switch from IgM synthesis only to the surface expression of other immunoglobulin classes without a change in antibody specificity (or V-region gene expression). Lastly, clones are selected for stimulation by antigen, or clones may be stimulated by polyclonal mitogens to divide and differentiate into plasma cells. Helper and suppressor T cells participate primarily in regulating the latter events.

TWO DISTINCT HUMAN T-CELL SUBPOPULATIONS: SUPPRESSOR ACTIVITY ON PWM-INDUCED B-CELL DIFFERENTIATION IS RESTRICTED TO T CELLS BEARING Fc-IgG RECEPTORS

Publisher Summary This chapter highlights two distinct human T-cell subpopulations that is suppressor activity on PWM-induced B-cell differentiation is restricted to T cells bearing Fc-IgG receptors. Up to 75% of human T lymphocytes from peripheral blood express receptors for IgM. T cells bearing receptors for IgG or IgM have been shown to belong to distinct cell populations with different responsiveness to PHA. In an earlier study described in the chapter, the T-cell dependency of pokeweed mitogen (PWM) induced B-cell proliferation and differentiation resides in the Tμ fraction, while Tγ cells can proliferate but do not help B-cell differentiation. Evidence has accumulated in a number of experimental systems for a regulatory role of suppressor T cells in antibody responses.

PROLIFERATIVE RESPONSIVENESS OF TWO DISTINCT HUMAN T-CELL SUBPOPULATIONS TO CON A, PHA AND ALLOANTIGENS

Publisher Summary This chapter discusses the proliferative responsiveness of two distinct human T-cell subpopulations to ConA, PHA, and alloantigens. It has been demonstrated that human T lymphocytes bear receptors for the Fc portion of IgG or IgM. T-cell subpopulations have been described on the basis of differential mitogen responsiveness. Tγ cells respond poorly at all concentrations of mitogen tested; the peak response is seen at low concentrations. In addition to Tμ and Tγ cells, there is a proportion of human T cells that do not express detectable receptors for either IgM or IgG. The addition of the responses of Tγ and Tγ-deprived cells observed at any given dose of PHA does not correspond to the response of the TT population.