Stewart C. Wang

Evidence for early Th 2 T cell predominance in xenoreactivity.

Two distinct subsets of CD4+ Th lymphocytes have been characterized by their cytokine profiles: Th 1 (TH1) and Th 2 (TH2). While TH1 cells predominate in cell-mediated responses, TH2 cells support the humoral response. We have examined the mRNA cytokine profile of normal mouse lymphocytes in response to alloantigen versus xenoantigen (rat) in MLC, and present evidence to suggest that early in proliferative responses, alloreactivity is dominated primarily by TH1-type lymphocytes, while xenoreactivity is predominantly TH2. Normal mouse lymphocyte-responding cells were cultured in a one-way MLR with either allo or xeno antigen and examined for production of mRNA for cytokines characteristically produced by TH1 (IL-2, IFN-γ) or TH2 (IL-4, IL-10) cells. Semiquantitative reverse transcription-polymerase chain reaction analysis was performed for mouse IL-2, IL-4, IL-10, and IFN-γ mRNA. In the mouse anti-rat xeno response, mRNA for TH2 gene products were upregulated, with greater levels of IL-4 and IL-10 at 24 and 48 hr when compared with controls. In contrast, upregulation of mRNA for TH1 gene products occurred in the mouse anti-mouse allo response, with higher levels of IL-2 and IFN-γ at 24 and 48 hr. In the anti-xeno response, upregulation of all 4 cytokines occurred by day 4 and peak levels of mRNA for all cytokines examined were 2—3 times that seen for the peak anti-allogeneic response. These data suggest that early xenorecognition may differ from allorecognition by differential activation of the TH2 subset. A better understanding of the balance between Th subset function and cytokine profile in allo and xeno reactivity may allow a more targeted and specific approach to control the early events in xenograft rejection.

Evidence that production of interleukin 6 within the rejecting allograft coincides with cytotoxic T lymphocyte development

Current evidence suggests that the development of allosensitized cytotoxic T lymphocytes within sponge matrix allografts takes place primarily in situ and may be regulated by the secretory products of the cells infiltrating the graft. In vitro studies have implicated IL-2, IL-4, and IL-6 in CTL development. We have reported that TNF-alpha, macrophage colony-stimulating factor, IL-1, IFN-alpha, and IFN-beta are present in the allograft, but that IL-2 and IL-4 cannot be detected at any time using specific bioassays. In this study, we found significantly higher levels of IL-6 within the allografts compared with the syngeneic grafts. Peak IL-6 activity coincided with the appearance of allosensitized CTL in the allografts. IL-6 concentration in the serum of sponge allografted mice was less than 1% of that found in the graft. The sponge fluid exhibited both hybridoma growth factor and hepatocyte-stimulating factor activities in vitro, and both these activities were neutralized by antibody to murine IL-6 but not by antibody to murine IL-1-beta or TNF-alpha. Messenger RNA for murine IL-6 was detected in the graft-infiltrating cells. The high level of IL-6 found in the allograft coincident with the appearance of cellular immunity suggests that this cytokine might play some role in the development of allospecific CTL in vivo.

Cyclic GMP and guanylate cyclase mediate lipopolysaccharide-induced Kupffer cell tumor necrosis factor-alpha synthesis.

Tumor necrosis factor‐α (TNF‐α) is an important mediator in sepsis and septic shock. Kupffer cells (KCs) are the resident macrophages of the liver and are potent producers of TNF‐α in response to inflammatory stimuli such as bacterial endotoxin or lipopolysaccharide (LPS). Although the effects of exogenous cytokines such as interferon‐γ on TNF‐α production by macrophages have been fairly well studied, the intracellular pathways regulating KC TNF‐α synthesis are largely unknown. We investigated the role of guanylate cyclase and cGMP in LPS‐induced KC TNF‐α synthesis. Exogenous 8‐BrcGMP and dbcGMP increased LPS‐stimulated TNF‐α synthesis but had no effect on KC TNF‐α in the absence of LPS. Sodium nitroprusside (SNP), a nitric oxide‐releasing substance that stimulates guanylate cyclase, increased TNF‐α synthesis in response to LPS, whereas methylene blue and LY83583, guanylate cyclase inhibitors, decreased KC TNF‐α synthesis. The inhibitory effect of methylene blue could be overcome with exogenous dbcGMP or SNP. Our results demonstrate that guanylate cyclase and cGMP mediate LPS‐induced KC TNF‐α synthesis and suggest that agents that alter cyclic nucleotide metabolism in KCs may affect the response of these cells to inflammation and inflammatory stimuli. J. Leukoc. Biol. 57: 297–302; 1995.

A dual mechanism of immunosuppression by FK-506. Differential suppression of IL-4 and IL-10 levels in T helper 2 cells.

FK-506 is known to suppress the transcription of several genes encoding cytokines (e.g., IL-2, IFN-γ) thought to play an important role in the allograft response. This general inhibition of cytokine gene transcription and protein production was previously thought to be the main mechanism by which FK-506 suppressed the immune response. We have studied the pattern of cytokine suppression caused by FK-506 in differentiated murine Th 2 cell lines. Supernatants from Th2 cells treated with FK-506 showed marked suppression of IL-4 but only moderate suppression of IL-10 levels. To determine whether this differential effect on IL-4 and IL-10 could also be seen at the mRNA level, total cellular RNA was isolated from cells treated with (1) media, (2) Con A (2 μg/ml), (3) FK-506 (50 ng/ml), or (4) Con A + FK-506. Reverse transcription-polymerase chain reaction and northern blot analysis were used to measure IL-4 and IL-10 mRNA. Similar to results at the protein level, FK-506 suppressed steady state levels of IL-4 mRNA markedly but had a lesser effect on steady state levels of IL-10 mRNA. Furthermore, FK-506 completely abrogated Con A-induced upregulation of IL-4 mRNA, but only slightly suppressed Con A-induced upregulation of IL-10 mRNA. IL-10 (cytokine synthesis inhibitory factor) is a cytokine with immunosuppressive properties that itself inhibits the production of IL-2 and IFN-γ by murine helper cells. IL-10 also downregulates MHC II expression and antigen presentation by monocytes. Therefore, the ability of FK-506 to differentially suppress the mRNA levels of immunostimulatory cytokines such as IL-2, IL-4, and IFN-γ more than the mRNA levels of the immunosuppressive cytokine IL-10 suggests that the effective immunosuppression seen in vivo with FK-506 may be a combination of these 2 effects.

FK-506 inhibits proliferation and IL-4 messenger RNA production by a T-helper 2 cell line

FK-506 is a potent immunosuppressant which is known to decrease the generation of allospecific cytotoxic T cells, possibly through its effect on cytokine production. FK-506 has been reported to have a suppressive effect on cytokine synthesis and secretion by pooled lymphocytes; its action on more selective subsets of lymphocytes is unknown. We currently report the effect of FK-506 on proliferation and IL-4 messenger RNA production by the differentiated mouse T-helper 2 cell line Ly1+2-/9. Ly1+2-/9 cells were grown in culture and treated with (1) media alone, (2) Con A, (3) FK-506, and (4) Con A + FK-506. Proliferation to Con A was determined by treating cells with 10 micrograms/ml Con A +/- FK-506 and measuring [3H]TdR uptake. Reverse transcriptase-polymerase chain reaction amplification was used to quantitate the level of IL-4 mRNA expression. FK-506 markedly inhibits Con A-induced proliferation and IL-4 mRNA production by the T-helper 2 cell line Ly1+2-/9. The ability of FK-506 to block the proliferation and IL-4 production by this helper cell subset suggests that this effect may contribute to its observed marked immunosuppressive properties in vitro and in vivo.

Induction of cytotoxic T lymphocyte development from murine thymocytes by IL-1 and IL-6

Cytotoxic T lymphocytes (CTL) are believed to play an important role in the regression of advanced malignancies in response to adoptive immunotherapy with interleukin-2 (IL-2) and lymphokine-activated killer cells or tumor-infiltrating lymphocytes. Because the current limitations to the use of adoptive immunotherapy are the IL-2 dose-dependent toxicities and the difficulty in expanding the effector cell population, recent investigations have focused on the development of newer methods for generating CTL in vitro. IL-1 and IL-6 have been shown to synergistically promote thymocyte proliferation; however, their effect on CTL development has not been studied. We investigated the ability of these two cytokines to induce CTL development from immature thymocytes. Thymocytes from 5-week-old BALB/c mice were cultured for 72 hours in the presence of Con A and recombinant IL-1, IL-6, or IL-1 plus IL-6. Cytotoxicity against 51Cr-labeled P815 target cells was then measured in the presence of submitogenic doses of PHA. Neither IL-1 nor IL-6 induced a significant number of CTL from immature thymocytes. However, these two cytokines synergistically induced maximal CTL development. The monoclonal antibody to IL-4 completely abrogated CTL development induced by IL-1 and IL-6, but antibody to the IL-2 receptor had no effect. The data suggest that IL-1 and IL-6 can provide an additional method for in vitro CTL generation in adoptive immunotherapy of advanced tumors.