Title

The effects of exogenous superantigens on human natural killer cells

Date of Award

1994

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Microbiology and Immunology

First Committee Member

Joan Stein-Streilein, Committee Chair

Abstract

This thesis examined the effects of two superantigens (sAgs), staphylococcal enterotoxin B (SEB) and Mycoplasma arthritidis mitogen (MAM) on human natural killer (NK) cells. Incubation of peripheral blood mononuclear cells (PBMC) with either sAg augmented NK cytotoxicity against NK-sensitive targets in a dose-dependent manner with the greatest augmentation occurring within the first 24 hours. Additionally, incubation of PBMC with SEB generated lymphokine-activated killer (LAK) activity. Although both sAgs consistently up-regulated NK activity in PBMC, MAM but not SEB increased lytic activity of sorted CD56$\sp+$ (i.e., NK) cells in a statistically significant manner (p $\leq$ 0.05). To understand which PBMC subpopulations were required for SEB-mediated killer induction of CD56$\sp+$ cells, cell mixing experiments were performed. When co-cultured with NK cells, purified T lymphocytes, but neither enriched monocytes nor the monocytic THP-1 cell line, supported the development of sAg-activated killer (SAK) activity. Further experiments revealed that in PBMC, generation of SAK activity was mediated by IL-2, IFN$\gamma$ and IL-12, and in co-cultures of NK and T cells, SAK induction was mediated by IL-2 and IFN$\gamma$. In addition, antibodies to major histocompatibility complex (MHC) class II HLA-D scR molecules blocked SAK induction in co-cultures of NK cells and T cells. When tested for their ability to present sAg, NK cells promoted SEB-mediated up-regulation of CD25 on T cells, and this presentation of SEB was dependent on MHC class II since depletion of class II-positive cells from the NK population prevented them from supporting SEB-induced T cell activation. NK cells also promoted cytokine production in response to sAg. Besides increasing the amount of IFN$\gamma$ in cultures of T cells and monocytes, NK cells produced IFN$\gamma$ in response to SEB by 72 h in the absence of other immune cells. Together, these data showed that exposure of PBMC to sAgs produced by certain bacteria and mycoplasma resulted in cytokine-dependent up-regulation of NK cytotoxicity, that NK cells presented sAg to T cells, and that NK cells produced IFN$\gamma$ in response to sAg.

Keywords

Biology, Microbiology; Health Sciences, Medicine and Surgery; Health Sciences, Immunology

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:9519726