Cloned Lymphoid Cell Lines

A primary lymphoid cell culture comprises a heterogeneous group of cells that can be propagated only for a limited time. This heterogeneity can complicate the interpretation of experimental results. To avoid these problems, immunologists use cloned lymphoid cell lines and hybrid cells.

Normal mammalian cells generally have a finite life span in culture; that is, after a number of population doublings characteristic of the species and cell type, the cells stop dividing. In contrast, tumor cells or normal cells that have undergone transformation induced by chemical carcinogens or viruses can be propagated indefinitely in tissue culture; thus, they are said to be immortal. Such cells are referred to as cell lines.

The first cell line—the mouse fibroblast L cell—was derived in the 1940s from cultured mouse subcutaneous connective tissue by exposing the cultured cells to a chemical carcinogen, methylcholanthrene, over a 4-month period. In the 1950s, another important cell line, the HeLa cell, was derived by culturing human cervical cancer cells. Since these early studies, hundreds of cell lines have been established, each consisting of a population of genetically identical (syngeneic) cells that can be grown indefinitely in culture.

Table 23-3 lists some of the cell lines used in immunologic research and briefly describes their properties. Some were derived from spontaneously occurring tumors of lymphocytes, macrophages, or other accessory cells involved in the immune response. In other cases, the cell line was induced by transformation of normal lymphoid cells with viruses such as Abelson's murine leukemia virus (A-MLV), simian virus 40

TABLE 23-3

Cell line

Cell lines commonly used in immunologic research

Description

L-929

SP2/0

P3X63-Ag8.653

MPC 11 P3X63-Ag8 MOPC 315 J558 7OZ/3

BCL 1

CTLL-2

Jurkat DO11.10

WEHI 265.1 P815

YAC-1

HL-60 COS-1

Mouse fibroblast cell line; often used in DNA transfection studies and to assay tumor necrosis factor (TNF)

Nonsecreting mouse myeloma; often used as a fusion partner for hybridoma secretion

Nonsecreting mouse myeloma; often used as a fusion partner for hybridoma secretion

Mouse IgG2b-secreting myeloma

Mouse IgG1-secreting myeloma

Mouse IgA-secreting myeloma

Mouse IgA-secreting myeloma

Mouse pre-B-cell lymphoma; used to study early events in B-cell differentiation

Mouse B-cell leukemia lymphoma that expresses membrane IgM and IgD and can be activated with mitogen to secrete IgM

Mouse T-cell line whose growth is dependent on IL-2; often used to assay IL-2 production

Human T-cell leukemia that secretes IL-2

Mouse T-cell hybridoma with specificity for ovalbumin

Mouse monocyte-macrophage line

Mouse monocyte-macrophage line that secretes high levels of IL-1

Mouse monocyte line

Mouse mastocytoma cells; often used as target to assess killing by cytotoxic T lymphocytes (CTLs)

Mouse lymphoma cells; often used as target for NK cells

Human myeloid-leukemia cell line

African green monkey kidney cells transformed by SV40; often used in DNA transfection studies

(SV40), Epstein-Barr virus (EBV), or human T-cell leukemia virus type 1(HTLV-1).

Lymphoid cell lines differ from primary lymphoid cell cultures in several important ways: They survive indefinitely in tissue culture, show various abnormal growth properties, and often have an abnormal number of chromosomes. Cells with more or less than the normal diploid number of chromosomes for a species are said to be aneuploid. The big advantage of cloned lymphoid cell lines is that they can be grown for extended periods in tissue culture, enabling im-munologists to obtain large numbers of homogeneous cells in culture.

Until the late 1970s, immunologists did not succeed in maintaining normal T cells in tissue culture for extended periods. In 1978, a serendipitous finding led to the observation that conditioned medium containing a T-cell growth factor was required. The essential component of the conditioned medium turned out to be interleukin 2 (IL-2). By cul-turing normal T lymphocytes with antigen in the presence of IL-2, clones of antigen-specific T lymphocytes could be isolated. These individual clones could be propagated and studied in culture and even frozen for storage. After thawing, the clones continued to grow and express their original antigen-specific functions.

Development of cloned lymphoid cell lines has enabled immunologists to study a number of events that previously could not be examined. For example, research on the molecular events involved in activation of naive lymphocytes by antigen was hampered by the low frequency of naive B and T cells specific for a particular antigen; in a heterogeneous population of lymphocytes, the molecular changes occurring in one responding cell could not be detected against a background of 103-106 nonresponding cells. Cloned T- and B-cell lines with known antigenic specificity have provided immu-nologists with large homogeneous cell populations in which to study the events involved in antigen recognition. Similarly, the genetic changes corresponding to different maturational stages can be studied in cell lines that appear to be "frozen" at different stages of differentiation. Cell lines have also been useful in studying the soluble factors produced by lymphoid cells. Some cell lines secrete large quantities of various cyto-kines; other lines express membrane receptors for particular cytokines. These cell lines have been used by immunologists to purify various cytokines and their receptors and eventually to clone their genes.

With the advantages of lymphoid cell lines come a number of limitations. Variants arise spontaneously in the course of prolonged culture, necessitating frequent subcloning to limit the cellular heterogeneity that can develop. If variants are selected in subcloning, it is possible that two subclones derived from the same parent clone may represent different subpopulations. Moreover, any cell line derived from tumor cells or transformed cells may have unknown genetic contributions characteristic of the tumor or of the transformed state; thus, researchers must be cautious when extrapolating results obtained with cell lines to the normal situation in vivo. Nevertheless, transformed cell lines have made a major contribution to the study of the immune response, and many molecular events discovered in experiments with transformed cell lines have been shown to take place in normal lymphocytes.

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  • Roisin Duncan
    What are hybrid lymphoid cell lines?
    8 years ago

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