Christoph H. Ladel

Role of T Cell Subsets in Immunity against Intracellular Bacteria: Experimental Infections of Knock-Out Mice with Listeria monocytogenes and Mycobacterium bovis BCG

The generation of knock-out mice with targeted gene deletions has already proven its enormous value for our understanding of the antimicrobial immune response. Here, we describe studies with knock-out mice deficient in the TCR-beta gene, lacking alpha/beta T cells; in the TCR-delta gene, lacking gamma/delta T cells; in the beta 2m gene, lacking beta 2-microglobulin, and hence cell surface expressed MHC class I and functional CD8 T cells; and in the H-2I-A beta gene, lacking cell surface expressed MHC class II and hence functional CD4 T cells. These mice were infected with Listeria monocytogenes or Mycobacterium bovis BCG as representative microbes which primarily activate CD8 T cells or CD4 T cells, respectively. Data described in this treatise demonstrate that the different gene deletions had an impact of varying degree on antibacterial defense and on the formation of granulomatous lesions. At the same time, the data point to a compensatory potential of the incomplete immune system. We assume that deletions in the major immune effector cells promote the emergence of a second line of defenders which frequently remain silent in the normal immune system. Thus, our data illustrate an enormous redundancy of the immune system, which, however, is not abundant since it takes over essential functions in the immunodeficient situation.

Participation of group 2 CD1 molecules in the control of murine tuberculosis

Besides the classical major histocompatibility complex (MHC) class I and MHC class II molecules, human CD1 molecules have been shown to present mycobacterial antigens in vitro. In this study, in vivo treatment of mice with anti-CD1 monoclonal antibodies resulted in exacerbated tuberculosis at very early time points. In CD1-modulated mice, Mycobacterium tuberculosis-specific production of the type 1 cytokines, IL-12, TNF, and IFN-gamma as well as of TGF beta was reduced. These findings suggest an antigen-presenting role of CD1 molecules in tuberculosis.

Application of knockout mice to the experimental analysis of infections with bacteria and protozoa

Knockout mice with distinct gene deletions are valuable tools for in vivo analyses of the immune response against infectious agents. Studies of bacterial and protozoal infections have shown that antimicrobial immunity is generally defective in knockout mice. At one extreme, deletion of just one gene may completely compromise resistance, while at the other extreme, redundancy in the immune system allows partial compensation for the deleted part.

Protein p60 Participates in Intestinal Host Invasion by Listeria monocytogenes

The role of p60 in intestinal invasion by Listeria monocytogenes was assessed after oral infection of mice with the p60 low-expressing mutant RIII, or with anti-p60 antibody coated wild-type EGD. Invasion by L. monocytogenes RIII bacteria has been unimpaired suggesting that a low density of p60 suffices for entry. Up to 24 h post infection (p.i.), intestinal penetration by L. monocytogenes EGD bacteria was markedly reduced by coating with anti-p60 antibodies. In histological sections, anti-p60 antibody-treated L. monocytogenes EGD, but not uncoated listeriae were still detectable 24 h p.i. at the apical surface of enterocytes in the intestine. We conclude that p60 contributes to host invasion through the natural port of listerial entry, the intestinal epithelium.

Localisation of human peripheral blood leukocytes after transfer to C.B-17 scid/scid mice

Severe combined immunodeficient (scid) mice of the inbred strain C.B-17 lack functional T and B cells and, because of this, they tolerate xenografts. We reconstituted scid mice with human peripheral blood leukocytes (PBL) by i.p. injection. In order to determine the human PBL in lymphoid organs of these reconstituted scid mice, we labelled the human PBL prior to transfer with the fluorescent dye PKH 26-GL. With this experimental approach it was possible to detect the human cells in lymphoid organs and peritoneal exudate of the reconstituted scid mice by cytofluorimetrical and histological methods. This method is thus helpful for the determination of xenografts transplanted upon scid mice as well as in other experimental settings including adoptive transfer.

Activation of natural killer cells by heat-killed Listeria monocytogenes requires additional signals from lymphoid cells.

Regulatory and protective functions have been attributed to murine natural killer (NK) cells in a number of infectious diseases including listeriosis. We have developed an in vitro model to study parameters underlying the activation of naive NK cells using heat-killed Listeria monocytogenes (HKL) as stimulator. Independent from expression of the cell surface marker NK1.1, NK cells lysed YAC-1 cells after in vitro stimulation with HKL or HKL + Interleukin (IL)-2, but not medium or IL-2 alone. In contrast, NK cells from severely immunocompromised SCID or RAG-1-/-mutant mice failed to respond to HKL alone, but required exogenous IL-2. Using single-gene-disruption mutant mice, we show that NK-cell activation can be supported by either T-cell receptor (TCR) alpha beta cells, TCR- gamma delta cells. MHC class I or MHC class II gene products. We conclude from these data that recognition of listerial components alone is insufficient for activation of naive NK cells, and that additional costimulatory signals are necessary. These can be provided by various lymphoid cells and appear to be cytokines.