Young adult type 1 diabetes care in the West of Ireland: an audit of hospital practice

BACKGROUND

It is well recognised that management of young adults with type 1 diabetes (T1DM) poses difficult challenges for physicians and health care organisations as a whole. In Ireland and in particular the west of Ireland there has been little audit or research on young adults with T1DM and the services available to them.

DESIGN

In 2011 a retrospective review of this patient population in our territory referral centre was carried out.

RESULTS

The average glycaemic control in this population was poor at 81mmols/mol and diabetes related complications were present in 32%. Engagement by this population with services was poor with an average of 3 missed clinic appointments over a 24 month period.

CONCLUSION

These results have prompted a re think of how health care professionals can deliver a service that better suits the needs of this challenging patient group.

Elevations of serum interleukin-12 concentrations in women with severe pre-eclampsia and HELLP syndrome

The objective is to test the hypothesis that serum IL-12 concentrations would be elevated in women with severe pre-eclampsia and HELLP syndrome. The Methods used were as follows: Serum was obtained from women admitted to our Labor and Delivery unit diagnosed with severe pre-eclampsia or HELLP syndrome and normal control patients. IL-12 concentrations in these samples were determined by the use of two different and specific enzyme-linked immunosorbent assays for the p40 subunit and the intact p75 dimer. It was found that serum IL-12 (p40 subunit) concentrations were elevated in women with both severe pre-eclampsia (p = 0.011) or HELLP syndrome (= 0.004). Similar findings were noted for these patients when matched with control patients for maternal age, gestational age, and parity. Eleven women had elevations of serum IL-12 p75 dimer, and 10 of these 11 patients had severe pre-eclampsia or HELLP syndrome. In conclusion, we found that women with severe pre-eclampsia and HELLP syndrome commonly have detectable concentrations of the IL-12 p40 monomer and were more likely than normal control women to have detectable serum IL-12 p75 dimer. While the exact role of IL-12 in hypertensive disease during pregnancy is unclear, our data support the hypothesis that the regulation of IL-12 production and metabolism is abnormal in women with pre-eclampsia and HELLP syndrome, perhaps contributing to the immunologic alterations characteristic of these disorders.

Down-regulating effects of IL-4 and IL-10 on the IFN-gamma response in atopic dermatitis

Atopic dermatitis (AD) is a chronic allergic disease associated with toxin (superantigen)-producing Staphylococcus aureus skin infections, impaired delayed hypersensitivity responses, and the expansion of IL-4-secreting Th2 cells, as well as diminished IFN-gamma synthesis. IL-12 is known to induce IFN-gamma synthesis and to augment Th1 responses. In this study, therefore, we examined the potential role of IL-12 in the immunopathogenesis of AD. We show that, after stimulation with staphylococcal toxic shock syndrome toxin-1 (TSST-1) or IL-12, PBMC from patients with AD are deficient in their ability to produce IFN-gamma. PBMC from AD patients, however, produced normal quantities of IL-12 and expressed normal levels of IL-12R. Induction of IFN-gamma by TSST-1 was decreased by neutralizing anti-IL-12 Ab in normal donors, but not in AD patients. The latter observation is consistent with a defective response to IL-12 in AD PBMC. Because AD is associated with increased production of IL-4 and IL-10, we examined the effect of IL-4 on IL-12- or TSST-1-induced IFN-gamma production in normal donors. IL-4 inhibited IL-12-induced IFN-gamma production. Furthermore, Ab neutralization of IL-4 caused increased production of IFN-gamma in AD PBMC. However, neutralization of IL-10 activity caused an even greater augmentation of IFN-gamma production. Our data suggest that despite normal levels of IL-12 production and IL-12R expression, PBMC from AD patients are unable to generate normal IL-12-induced IFN-gamma responses. This defective response may be due to the excess production of IL-4 and IL-10 in this common allergic condition.

Down-regulating effects of IL-4 and IL-10 on the IFN-gamma response in atopic dermatitis

Atopic dermatitis (AD) is a chronic allergic disease associated with toxin (superantigen)-producing Staphylococcus aureus skin infections, impaired delayed hypersensitivity responses, and the expansion of IL-4-secreting Th2 cells, as well as diminished IFN-gamma synthesis. IL-12 is known to induce IFN-gamma synthesis and to augment Th1 responses. In this study, therefore, we examined the potential role of IL-12 in the immunopathogenesis of AD. We show that, after stimulation with staphylococcal toxic shock syndrome toxin-1 (TSST-1) or IL-12, PBMC from patients with AD are deficient in their ability to produce IFN-gamma. PBMC from AD patients, however, produced normal quantities of IL-12 and expressed normal levels of IL-12R. Induction of IFN-gamma by TSST-1 was decreased by neutralizing anti-IL-12 Ab in normal donors, but not in AD patients. The latter observation is consistent with a defective response to IL-12 in AD PBMC. Because AD is associated with increased production of IL-4 and IL-10, we examined the effect of IL-4 on IL-12- or TSST-1-induced IFN-gamma production in normal donors. IL-4 inhibited IL-12-induced IFN-gamma production. Furthermore, Ab neutralization of IL-4 caused increased production of IFN-gamma in AD PBMC. However, neutralization of IL-10 activity caused an even greater augmentation of IFN-gamma production. Our data suggest that despite normal levels of IL-12 production and IL-12R expression, PBMC from AD patients are unable to generate normal IL-12-induced IFN-gamma responses. This defective response may be due to the excess production of IL-4 and IL-10 in this common allergic condition.

Activated T cells induce interleukin-12 production by monocytes via CD40-CD40 ligand interaction

Previous studies on the production of interleukin-12 (IL-12) have shown that it is released, together with other proinflammatory cytokines, shortly after exposure of phagocytic cells to a variety of pathogens. We here report that IL-12 is also released during the recall response to soluble antigen (Ag) devoid of intrinsic adjuvant activity. We show that activated T cells induce the production of IL-12 by monocytes via a mechanism involving the interaction of T cell-associated CD40 ligand with CD40 on monocytes. The data suggest that Ag presentation on monocytes favors the persistence of type 1 responses.

Bacterial superantigens induce T cell expression of the skin-selective homing receptor, the cutaneous lymphocyte-associated antigen, via stimulation of interleukin 12 production

T lymphocyte infiltration is a prominent feature of the skin inflammation associated with infections by toxin (superantigen)-secreting Staphylococcus aureus or Streptococcus bacteria. The cutaneous lymphocyte-associated antigen (CLA) has been hypothesized to be a homing receptor (HR) involved in selective migration of memory/effector T cells to the skin. Since the expression of this putative skin-selective HR is known to be under strict microenvironmental control, we sought to determine the effect of staphylococcal and streptococcal toxins on T cell expression of CLA. After in vitro stimulation of peripheral blood mononuclear cells with staphylococcal enterotoxin B, toxic shock syndrome toxin-1, and streptococcal pyrogenic exotoxins A and C, there was a significant increase in the numbers of CLA+ T cell blasts (p < 0.01), but not blasts bearing the mucosa-associated adhesion molecule alpha e beta 7-integrin, compared with T cells stimulated with phytohemaglutinin (PHA) or anti-CD3. Bacterial toxins were also found to specifically induce interleukin (IL) 12 production. More importantly, induction of toxin-induced CLA expression was blocked by anti-IL-12, and the addition of IL-12 to PHA-stimulated T cells induced CLA, but not alpha e beta 7-integrin, expression. These data suggest that bacterial toxins induce the expansion of skin-homing CLA+ T cells in an IL-12-dependent manner, and thus may contribute to the development of skin rashes in superantigen-mediated diseases.

Construction and characterization of retroviral vectors expressing biologically active human interleukin-12

Interleukin-12 (IL-12) is a heterodimeric cytokine originally defined by its ability to induce the maturation of cytolytic lymphocytes and by its capacity to effectively synergize with IL-2 in the induction of cytolytic activity. Recent studies in mice have demonstrated the ability of IL-12 to cause tumor regression and stimulate long-term antitumor immunity in treated animals. To examine the antitumor effect of direct gene transfer of IL-12 into tumors, we have developed retroviral vectors that coordinately express both subunits of IL-12. An MFG-based retroviral vector was used to generate a recombinant retrovirus in which a long terminal repeat (LTR)-driven polycistronic transcript encodes both subunits of human IL-12: hp35 and hp40 cDNAs are linked and coexpressed using the internal ribosome entry site (IRES) from the encephalomyocarditis virus (DFG-hIL-12). In addition, two IRES sequences were used to express both subunits of IL-12 and a neomycin resistance (neoR) selectable marker gene from the same polycistronic message (TFG-hIL-12). The amphotropic DFG-hIL-12 and TFG-hIL-12 viruses were used to infect both human and murine cell lines as well as primary tumor cultures. The production of human IL-12 by the nonselected, infected cells was measured in both a PHA blast proliferation bioassay and an ELISA and ranged from 15 to 40 ng/10(6) cells per 24 hr. Following G418 selection of TFG-hIL-12-infected cells, the level of expression of IL-12 was significantly higher (up to 120 ng/10(6) cells per 24 hr). The IL-12 protein secreted by the infected cells exhibited all of the biologic activities of recombinant hIL-12: proliferation of activated natural killer (NK) and T cells, stimulation of interferon-gamma (IFN-gamma) induction by NK and T cells, and enhancement of lymphokine-activated killer (LAK) activity. These retroviral vectors expressing human IL-12 should be useful in evaluating the biological properties of IL-12 as well as for use in clinical trials for gene therapy of patients with cancer.

Interleukin 12, interferon gamma, and tumor necrosis factor alpha are the key cytokines of the generalized Shwartzman reaction

The Shwartzman reaction is elicited by two injections of lipopolysaccharide (LPS) in mice. The priming LPS injection is given in the footpad, whereas the lethal LPS challenge is given intravenously 24 h later. The injection of interferon gamma (IFN-gamma) or interleukin 12 (IL-12) instead of the LPS priming injection induced the lethal reaction in mice further challenged with LPS. Antibodies against IFN-gamma when given together with the priming agent, prevented the lethal reaction in mice primed with either LPS, IL-12, or IFN-gamma. Antibodies against IL-12, when given together with the priming agent, prevented the lethal reaction in mice primed with either LPS or IL-12 but not with IFN-gamma. These results strongly suggest that LPS induces the release of IL-12, that IL-12 induces the production of IFN-gamma, and that IFN-gamma is the cytokine that primes macrophages and other cell types. Upon LPS challenge, the lethal Shwartzman reaction is induced by a massive production of inflammatory cytokines that act on the target sites already sensitized by IFN-gamma. If mixtures of TNF and IL-1 or mixtures of TNF and IFN-gamma are used to challenge mice previously primed with IFN-gamma or IL-12, mortality is induced. In the same conditions, the individual cytokines or a mixture of IL-1 and IFN-gamma do not replace the LPS challenge. When the mice are primed with LPS, the combination of TNF, IL-1, and IFN-gamma induced only a partial mortality incidence suggesting that the involvement of other LPS-induced factors.

In vitro maturation of human neonatal CD4 T lymphocytes. I. Induction of IL-4-producing cells after long-term culture in the presence of IL-4 plus either IL-2 or IL-12

Recent studies in the mouse have established that IL-4 and IL-12 direct the development of Ag-stimulated naive CD4 T cells into, respectively, type 2 and type 1 Th cells. We report that prolonged exposure of immunologically naive and unstimulated human neonatal CD4 T cells to IL-4 or to IL-4 plus either IL-2 or IL-12 markedly affects their cytokine production on primary stimulation with PMA and ionomycin. IL-4 induces long-term proliferation of neonatal T cells and after 3 wk of culture these are capable of producing high levels of Th1 (IL-2, IFN-gamma) but no Th2 (IL-4, IL-5) cytokines; IL-4-primed cells are homogenously CD45RO-/RA+ and CD31+. After culture in the presence of IL-4 + IL-2 or IL-4 + IL-12, neonatal T cells are enriched in CD45RO+ and CD31- cells and they can produce Th2 as well as Th1 cytokines. In response to primary stimulation with PMA and ionomycin, cells primed with IL-4 + IL-2 produce IL-4, IL-5, and IL-10 and the same levels of IL-2 and IFN-gamma as IL-4-primed cells. Cells primed with IL-4 + IL-12 produce very high levels of both IL-4 and IFN-gamma but no IL-5. Endogenous IFN-gamma that is detected in primary cultures containing IL-4 + IL-12 does not inhibit, but rather enhances, the ability of the cells to produce IL-4. Further analysis of IL-4 + IL-12-primed cells reveals that IL-4 is mainly produced by CD31- cells and that these cells can trigger B cells to synthesize Ig including IgE. Finally, positively selected CD31+ cells remain CD31+ and are poor IL-4 producers after 3 wk of culture with IL-4 + IL-12, suggesting that these two cytokines promote the selective expansion of the small number of CD31- cells that are present in freshly isolated neonatal CD4 T cells.

In vitro maturation of human neonatal CD4 T lymphocytes. I. Induction of IL-4-producing cells after long-term culture in the presence of IL-4 plus either IL-2 or IL-12

Recent studies in the mouse have established that IL-4 and IL-12 direct the development of Ag-stimulated naive CD4 T cells into, respectively, type 2 and type 1 Th cells. We report that prolonged exposure of immunologically naive and unstimulated human neonatal CD4 T cells to IL-4 or to IL-4 plus either IL-2 or IL-12 markedly affects their cytokine production on primary stimulation with PMA and ionomycin. IL-4 induces long-term proliferation of neonatal T cells and after 3 wk of culture these are capable of producing high levels of Th1 (IL-2, IFN-gamma) but no Th2 (IL-4, IL-5) cytokines; IL-4-primed cells are homogenously CD45RO-/RA+ and CD31+. After culture in the presence of IL-4 + IL-2 or IL-4 + IL-12, neonatal T cells are enriched in CD45RO+ and CD31- cells and they can produce Th2 as well as Th1 cytokines. In response to primary stimulation with PMA and ionomycin, cells primed with IL-4 + IL-2 produce IL-4, IL-5, and IL-10 and the same levels of IL-2 and IFN-gamma as IL-4-primed cells. Cells primed with IL-4 + IL-12 produce very high levels of both IL-4 and IFN-gamma but no IL-5. Endogenous IFN-gamma that is detected in primary cultures containing IL-4 + IL-12 does not inhibit, but rather enhances, the ability of the cells to produce IL-4. Further analysis of IL-4 + IL-12-primed cells reveals that IL-4 is mainly produced by CD31- cells and that these cells can trigger B cells to synthesize Ig including IgE. Finally, positively selected CD31+ cells remain CD31+ and are poor IL-4 producers after 3 wk of culture with IL-4 + IL-12, suggesting that these two cytokines promote the selective expansion of the small number of CD31- cells that are present in freshly isolated neonatal CD4 T cells.

IL-12 induces the production of IFN-gamma by neonatal human CD4 T cells

A major difference between "naive" and "memory" or "effector" Th cells is the spectrum of cytokines that they are capable of producing. After stimulation naive cells produce only IL-2, whereas memory cells produce several cytokines including IFN-gamma and IL-4. Using umbilical cord blood-derived CD4 T cells as a source of naive T cells, we first report that these cells are capable of producing large amounts of IFN-gamma when cultured with low concentrations of IL-12. The response is time- and dose-dependent, and it is observed at the protein and mRNA levels. IL-12 also induces neonatal CD4 T cells to produce lymphotoxin but not IL-2, TNF-alpha, or IL-4. The production of IFN-gamma by IL-12-stimulated neonatal T cells is associated with a small but significant T cell activation evidenced by DNA synthesis and by the expression of the activation markers CD25, CD71, and HLA-DR; moreover, it is inhibited by hydrocortisone, cyclosporin A, and transforming growth factor-beta. The response to IL-12 is enhanced and is much more rapid when CD4 T cells are cultured in the presence of accessory cells or of exogenous IL-1, IL-2, or TNF-alpha. Using a three-step culture system, we next show that IL-12 induces the maturation of resting naive CD4 T cells into cells producing both IL-2 and IFN-gamma but not IL-4 upon stimulation with PMA and ionomycin. Endogenously produced IFN-gamma plays a role in this IL-12-induced T cell maturation, as shown by the inhibitory effect of neutralizing IFN-gamma antibodies. Finally, we show that IL-12 supports the production of IFN-gamma during primary stimulation of neonatal T cells via the CD3/TCR complex by means of either immobilized anti-CD3 mAb or superantigen-coated (Staphylococcus enterotoxin B) fixed L cell transfectants expressing HLA-DR. It is suggested that IL-12 is involved in the selection of Th1 type immune responses.

IL-12 induces the production of IFN-gamma by neonatal human CD4 T cells

A major difference between "naive" and "memory" or "effector" Th cells is the spectrum of cytokines that they are capable of producing. After stimulation naive cells produce only IL-2, whereas memory cells produce several cytokines including IFN-gamma and IL-4. Using umbilical cord blood-derived CD4 T cells as a source of naive T cells, we first report that these cells are capable of producing large amounts of IFN-gamma when cultured with low concentrations of IL-12. The response is time- and dose-dependent, and it is observed at the protein and mRNA levels. IL-12 also induces neonatal CD4 T cells to produce lymphotoxin but not IL-2, TNF-alpha, or IL-4. The production of IFN-gamma by IL-12-stimulated neonatal T cells is associated with a small but significant T cell activation evidenced by DNA synthesis and by the expression of the activation markers CD25, CD71, and HLA-DR; moreover, it is inhibited by hydrocortisone, cyclosporin A, and transforming growth factor-beta. The response to IL-12 is enhanced and is much more rapid when CD4 T cells are cultured in the presence of accessory cells or of exogenous IL-1, IL-2, or TNF-alpha. Using a three-step culture system, we next show that IL-12 induces the maturation of resting naive CD4 T cells into cells producing both IL-2 and IFN-gamma but not IL-4 upon stimulation with PMA and ionomycin. Endogenously produced IFN-gamma plays a role in this IL-12-induced T cell maturation, as shown by the inhibitory effect of neutralizing IFN-gamma antibodies. Finally, we show that IL-12 supports the production of IFN-gamma during primary stimulation of neonatal T cells via the CD3/TCR complex by means of either immobilized anti-CD3 mAb or superantigen-coated (Staphylococcus enterotoxin B) fixed L cell transfectants expressing HLA-DR. It is suggested that IL-12 is involved in the selection of Th1 type immune responses.

Recombinant interleukin-12 suppresses the synthesis of immunoglobulin E by interleukin-4 stimulated human lymphocytes

Interleukin-12 is a recently discovered lymphokine displaying an array of in vitro activities suggesting a major role in protective immunity against infectious agents like viruses. This study provides evidence that IL-12 may also be implicated in the selection of the immunoglobulin isotypes. We show that picomolar concentrations of rIL-12 markedly inhibit the synthesis of IgE by IL-4-stimulated PBMC. The suppression of IgE is observed at the protein and at the mRNA levels, it is isotype specific, and it is abolished by neutralizing anti-IL-12 mAbs. IL-12 may suppress IgE synthesis by: (a) inducing the production of IFN-gamma, a known inhibitor of IgE synthesis and (b) by a novel mechanism which is IFN-gamma independent. The best evidence for this is from studies on IgE synthesis by IL-4-plus hydrocortisone-stimulated umbilical cord blood lymphocytes, which do not produce detectable amounts of IFN-gamma. In such cultures, rIL-12 inhibits IgE synthesis even in the presence of a large excess of neutralizing anti-IFN-gamma mAb.

A comparative study of IL-12 (cytotoxic lymphocyte maturation factor)-, IL-2-, and IL-7-induced effects on immunomagnetically purified CD56+ NK cells

IL-12, or cytotoxic lymphocyte maturation factor, is a recently cloned cytokine shown to influence lymphokine-activated killer cells activity in heterogeneous lymphocyte populations, proliferative activity as a costimulus in PBMC/PBL populations and IFN-gamma production in PBL. We have investigated the effects of IL-12 on immunomagnetically highly purified CD56+ lymphocytes, and compared the effects with those of IL-7 and IL-2. Our results show that IL-12 directly generated high lymphokine-activated killer cell activity in CD56+ NK cells, without the need for accessory cells. The IL-12-induced lymphokine-activated killer cell activity reached 50% of what was obtained with IL-2. In contrast, only low proliferative activity was induced by IL-12, as 10% of the IL-2-induced- and approximately 50% of the IL-7-induced proliferative activity was detected with IL-12. The CD56+ cells expressed high levels of IL-2R alpha and 75-kDa TNFR in response to IL-12, comparable to what was registered with IL-2 and IL-7. Furthermore, an extensive up-regulation of the CD56 Ag, to the level obtained with IL-2, was detected in the CD56+ NK cells in the presence of IL-12. Stimulation with IL-7 resulted in a more limited CD56 up-regulation in the CD56+ NK cells. Low concentrations of TNF-alpha were produced in response to both IL-12 and IL-7, with little or no TNF-beta production. Time course of the IL-2-induced TNF production revealed an initial TNF-alpha production, whereas significant levels of TNF-beta were detected after 72 h. The effects of both IL-12 and IL-7 on the CD56+ NK cells were inhibited by an anti-TNF-alpha mAb. Thus, IL-12 can directly influence NK cell activities in purified CD56+ cells, and endogenously produced TNF-alpha is involved in mediating the effects of both IL-12 and IL-7.

A comparative study of IL-12 (cytotoxic lymphocyte maturation factor)-, IL-2-, and IL-7-induced effects on immunomagnetically purified CD56+ NK cells

IL-12, or cytotoxic lymphocyte maturation factor, is a recently cloned cytokine shown to influence lymphokine-activated killer cells activity in heterogeneous lymphocyte populations, proliferative activity as a costimulus in PBMC/PBL populations and IFN-gamma production in PBL. We have investigated the effects of IL-12 on immunomagnetically highly purified CD56+ lymphocytes, and compared the effects with those of IL-7 and IL-2. Our results show that IL-12 directly generated high lymphokine-activated killer cell activity in CD56+ NK cells, without the need for accessory cells. The IL-12-induced lymphokine-activated killer cell activity reached 50% of what was obtained with IL-2. In contrast, only low proliferative activity was induced by IL-12, as 10% of the IL-2-induced- and approximately 50% of the IL-7-induced proliferative activity was detected with IL-12. The CD56+ cells expressed high levels of IL-2R alpha and 75-kDa TNFR in response to IL-12, comparable to what was registered with IL-2 and IL-7. Furthermore, an extensive up-regulation of the CD56 Ag, to the level obtained with IL-2, was detected in the CD56+ NK cells in the presence of IL-12. Stimulation with IL-7 resulted in a more limited CD56 up-regulation in the CD56+ NK cells. Low concentrations of TNF-alpha were produced in response to both IL-12 and IL-7, with little or no TNF-beta production. Time course of the IL-2-induced TNF production revealed an initial TNF-alpha production, whereas significant levels of TNF-beta were detected after 72 h. The effects of both IL-12 and IL-7 on the CD56+ NK cells were inhibited by an anti-TNF-alpha mAb. Thus, IL-12 can directly influence NK cell activities in purified CD56+ cells, and endogenously produced TNF-alpha is involved in mediating the effects of both IL-12 and IL-7.

IL2-PE664Glu, a new chimeric protein cytotoxic to human-activated T lymphocytes

To produce a molecule that will kill activated T cells as well as lymphomas and leukemias expressing interleukin 2 (IL2) receptors, we have created a recombinant chimeric protein in which IL2 is attached in peptide linkage to a truncated mutant form of Pseudomonas exotoxin (PE) (Lorberboum-Galski, H., FitzGerald, D.J.P., Chandhary, V.K., Adhya, S., and Pastan, I. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 1922-1926). Although this molecule was very active on rodent cells, it had lower activity on some human cell types. A new chimeric protein termed IL2-PE664Glu has been constructed that is extremely toxic to both phytohemagglutinin blasts and mixed leukocyte reaction blasts prepared from monkey and human lymphocytes. The chimeric gene encoding this protein was constructed by fusing a cDNA clone for human interleukin 2 to the 5' end of a mutated cDNA encoding a full-length PE molecule. Four amino acids in domain I of PE were changed thus decreasing its nonspecific toxicity. IL2-PE664Glu is a much more active cytotoxic molecule for primate and human-activated T cells than IL2-PE40 which is a chimeric protein that was found to be an effective immunosuppressive agent in rodent models. Our results indicate that IL2-PE664Glu should be evaluated as an immunosuppressive agent for the treatment of human immune disorders in which activated T cells expressing the IL2 receptor are prominent.

Anti-Tac(Fv)-PE40, a single chain antibody Pseudomonas fusion protein directed at interleukin 2 receptor bearing cells

Anti-Tac(Fv)-PE40 is a chimeric single chain immunotoxin in which anti-Tac variable heavy and light chains held together by a peptide linker are attached to PE40, a truncated form of Pseudomonas exotoxin. This molecule was shown to be extremely cytotoxic for interleukin 2 (IL2) receptor bearing cells in tissue culture (Chaudhary, V. K., Queen, C., Junghans, R. P., Waldmann, T. A., FitzGerald, D. J., and Pastan, I. (1989) Nature 339, 394-397). Here we describe various forms of anti-Tac(Fv)-PE40 protein in which the order of the variable domains of anti-Tac has been switched and also three different types of peptide linkers have been used. All these proteins were purified to near homogeneity and were found to have similar cytotoxic activities against various human cells expressing the p55 subunit of the IL2 receptor. Anti-Tac(Fv)-PE40 was also found to have a very potent suppressive activity against phytohemagglutinin-activated human lymphoblasts and in a human mixed lymphocyte reaction. Anti-Tac(Fv)-PE40 appeared in the blood rapidly in mice after intraperitoneal administration and could be detected in the blood for up to 8 h. Anti-Tac(Fv)-PE40 warrants evaluation as an anti-tumor and immunosuppressive agent in humans.