Stromal-Cell and Cytokine-Dependent Lymphocyte Clones Which Span the Pre-B- to B-Cell Transition

Five stromal-cell-dependent lymphocyte clones are described that correspond to late pre-B or early B-cell stages of differentiation.They are useful for determining the molecular requirements for pre-B replication, for studying the stromal cells that supply those factors, and for delineating the final sequence of differentiation events as newly formed lymphocytes prepare to exit the bone marrow. The efficiency of lymphocyte growth at limiting dilution varied substantially on different stromal-cell clones and may reflect functional heterogeneity of stromal cells. Most lymphocyte clones were similar to uncloned lymphocytes from Whitlock-Witte cultures in that they responded only transiently to interleukin-7 (IL-7) and then died, unless maintained on a stromal-cell clone. One unusual lymphocyte clone (2E8) was propagated for more than 1 year in IL-7 alone and was selectively responsive to that cytokine. Most of the lymphocyte clones were not tumorigenic in immunodeficient mice. However, one pre-B clone (1A9)’grew autonomously in culture when held at high density, responded to conditioned medium from a number of cell lines, and was tumorigenic. Tumors derived from this clone were infiltrated by stromal cells and lymphocytes taken from the tumors' retained characteristics of the original clone. Ly-6 antigens were inducible on 2E8 and 1A9 cells, but the lymphocytes were otherwise arrested in differentiation. The 2E8 cells had rearranged and expressed κ light-chain genes but displayed them on the surface along with surrogate light chains and μ heavy chains. Thus, expression of authentic Tight chain need not coincide with termination of surrogate light-chain utilization in newly formed B cells. Several glycoproteins have recently been demonstrated to be associated with surface immunoglobulin (Ig) on mature B-lineage cells and plasma-cell tumors. We now show that one member of this family (approximately 33 kD) was associated with the μ+surrogate light-chain complex on the 1A9 pre-B-cell clone. When compared to mature B lymphomas, fewer bands coprecipitated with the surface-labeled Ig isolated from pre-B- and early B-cell lines, suggesting that components of the antigen receptor are sequentially acquired during development. The normal replication and differentiation of pre-B cells is probably regulated by complex interactions with multiple cytokines and matrix components of the marrow microenvironment. Cloned lymphocyte lines that are dependent on stromal cells should continue to be important tools for molecular definition of those interactions

Mechanism of resistance to Listeria monocytogenes in splenectomized mice

The present study is an investigation of the basis of the enhanced antilisterial resistance exhibited by splenectomized mice. The response of the mononuclear phagocyte system of these hosts has been extensively investigated as a result of the finding that enhanced antilisterial resistance in these hosts is abolished by treatment with silica. Splenectomized mice demonstrate a quantitatively greater influx of immature macrophage precursors in response to listerial infection and intraperitoneal stimuli. Despite the higher responsiveness of immature macrophage precursors in the splenectomized host, radiation studies have determined that antilisterial resistance in splenectomized mice is provided by the mature mononuclear phagocytes of the liver, the Kupffer cells. However, Kupffer cells of splenectomized mice exhibit the same level of function associated with listericidal activity as non-splenectomized animals. An examination of the cellular composition of the spleen at early time intervals following infection with Listeria has led to the conclusion that enhanced antilisterial resistance in splenectomized mice may be explained on the basis of the loss of a storage function of the spleen. In the absence of the spleen, leucocytes are made available for migration to the liver upon infection of the host. The early destruction of Listeria which presumably results, is responsible for the lower growth of the organism measured at 48 hours post-infection

Characteristics of Mononuclear Phagocytes Mediating Antilisterial Resistance in Splenectomized Mice

The characteristics of mononuclear phagocytes mediating resistance to infection with Listeria monocytogenes during the early phase (up to 48 h) of the response were investigated in mice of the A strain that had undergone splenectomy. Although irradiation in the sham-operated host had no effect on its antilisterial response when administered immediately before infection, it markedly reduced the ability of the splenectomized host to resist listerial challenge. This effect of radiation was demonstrable in the high-dose range (600 r) and could not be reversed immediately by repopulation with 20 × 10(6) syngeneic nucleated bone marrow cells. Administration of silica 24 h before infection profoundly enhanced the growth of L. monocytogenes in the liver of splenectomized mice. Shielding of the liver, but not the bone marrow, protected the splenectomized host against the effects of radiation, indicating that the cell population responsible for mediating the enhanced antilisterial resistance resides in the liver. The enhanced antilisterial resistance of splenectomized mice was specifically because of the absence of the spleen and not merely because of the removal of a favorable replicating environment for listeria organisms