Pyroptosis is a form of lytic programmed cell death initiated by inflammasomes, which detect cytosolic contamination or perturbation. This drives activation of caspase-1 or caspase-11/4/5, which cleave gasdermin D, separating its N-terminal pore-forming domain (PFD) from the C-terminal repressor domain (RD). The PFD oligomerizes to form large pores in the membrane that drive swelling and membrane rupture. Gasdermin D is one of six (in humans) gasdermin family members; several other gasdermins have also been shown to form pores that cause pyroptosis after cleavage to activate their PFDs. One of these, gasdermin E, is activated by caspase-3 cleavage. We review our current understanding of pyroptosis as well as current knowledge of the gasdermin family.

SUMMARY Either caspase-1 or caspase-11 can cleave gasdermin D to cause pyroptosis, eliminating intracellular replication niches. We previously showed that macrophages detect Burkholderia thailandensis via NLRC4, triggering the release of interleukin (IL)-18 and driving an essential interferon (IFN)-γ response that primes caspase-11. We now identify the IFN-γ-producing cells as a mixture of natural killer (NK) and T cells. Although both caspase-1 and caspase-11 can cleave gasdermin D in macrophages and neutrophils, we find that NLRC4-activated caspase-1 triggers pyroptosis in macrophages, but this pathway does not trigger pyroptosis in neutrophils. In contrast, caspase-11 triggers pyroptosis in both macrophages and neutrophils. This translates to an absolute requirement for caspase-11 in neutrophils during B. thailandensis infection in mice. We present an example of inflammasome sensors causing diverging outcomes in different cell types. Thus, cell fates are dictated not simply by the pathogen or inflammasome, but also by how the cell is wired to respond to detection events.

During acute human immunodeficiency virus (HIV) infection, there is a massive depletion of CD4؉ T cells in the gut mucosa that can be reversed to various degrees with antiretroviral therapy. -infected individuals treated with prolonged antiretroviral therapy (ART) (VL [viral load]<50). We found that LTNPs have intact CD4؉ T cell populations, including Th17 and cycling subsets, in the gut mucosa and a preserved T cell population expressing gut homing molecules in the peripheral blood. In addition, we observed no evidence of higher monocyte activation in LTNPs than in HIV-infected (HIV ؊ ) controls. These data suggest that, similar to nonpathogenic simian immunodeficiency virus (SIV) infection, LTNPs preserve the balance of CD4 ؉ T cell populations in blood and gut mucosa, which may contribute to the lack of disease progression observed in these patients.

Key Points rhIL-7 therapy was well tolerated in patients with ICL. rhIL-7 led to increases in CD4 T cells in both peripheral blood and tissues.

Idiopathic CD4(+) lymphopenia (ICL) is a rare syndrome characterized by low peripheral CD4(+) T-cell counts that can lead to serious opportunistic infections. The pathogenesis of ICL remains unclear, and whether effector sites are also lymphopenic is unknown. In this study, rectosigmoid mucosal biopsy specimens from patients with ICL and healthy controls were evaluated. Significant T-cell lymphopenia was observed in the mucosal tissue of patients with ICL by flow cytometry and immunohistochemistry, compared with healthy controls. Functional capacity of T cells, assessed by production of interferon γ and interleukin 17, was preserved in the mucosa of patients with ICL. In contrast to T lymphocytes, the frequency of myeloid cells (neutrophils and macrophages) was elevated in the colonic mucosa of patients with ICL. Despite the observed mucosal abnormalities, plasma levels of intestinal fatty acid binding protein, a marker of enterocyte turnover and other inflammatory biomarkers, including interleukin 6, C-reactive protein, and tumor necrosis factor, were not elevated in patients with ICL, compared with healthy controls, whereas soluble CD14 levels were minimally elevated. These data suggest that patients with ICL, despite gut mucosal lymphopenia and local tissue inflammation, have preserved enterocyte turnover and T-helper type 17 cells with minimal systemic inflammation. These observations highlight differences from patients with human immunodeficiency virus infection, with or without AIDS, and may partially explain their distinct clinical prognosis.

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Herpes simplex virus type 1 (HSV-1) infection can manifest locally as mucocutaneous lesions or keratitis and can also spread to the central nervous system to cause encephalitis. HSV-1 establishes a lifelong latent infection and neither cure nor vaccine is currently available. The innate immune response is the first line of defense against infection. Caspases and gasdermins are important components of innate immunity. Caspases are a family of cysteine proteases, most of which mediate regulated cell death. Gasdermins are a family of pore-forming proteins that trigger lytic cell death. To determine whether caspases or gasdermins contribute to innate immune defenses against HSV-1, we screened mice deficient in specific cell death genes. Our results indicate a modest role for caspase-6 in defense against HSV-1. Further, Asc–/–Casp1/11–/– mice also had a modest increased susceptibility to HSV-1 infection. Caspase-7, -8, and -14 did not have a notable role in controlling HSV-1 infection. We generated Gsdma1-Gsdma2-Gsdma3 triple knockout mice, which also had normal susceptibility to HSV-1. We confirmed that the previously published importance of RIPK3 during systemic HSV-1 infection also holds true during skin infection. Overall, our data highlight that as a successful pathogen, HSV-1 has multiple ways to evade host innate immune responses.

Background: Despite antiretroviral therapy (ART), people with HIV continue to exhibit immune deficits including failure to fully reconstitute CD4 T cell numbers and function, resulting in increased risks of tumors and infections and reduced response to vaccination. Pomalidomide, a derivative of thalidomide (IMID), has immunomodulatory properties that may be beneficial in this setting. We explored its impact on lymphocyte number and activation in patients with and without HIV treated within a prospective clinical trial for Kaposi sarcoma. Methods: Patients received pomalidomide 5mg orally for 21 days of 28 day cycles. Assessments were performed every 4 weeks for lymphocyte numbers, Kaposi sarcoma associated herpesvirus (KSHV/HHV8) viral load (VL) and HIV VL and at 8 weeks for T cell subsets and activation by immunophenotyping of peripheral blood mononuclear cells (PBMC). KSHV VL in PBMC and HIV VL in plasma were assayed by quantitative PCR; for HIV VL we used an ultrasensitive single copy assay. Changes from baseline were evaluated using the Wilcoxon signed rank test with P<0.005 considered significant given multiple comparisons. Differences in changes between the HIV infected and uninfected groups were evaluated using the Wilcoxon rank sum test. Study registered as NCT1495598. Results: 19 patients (12 HIV infected, 7 uninfected) median age 50 years (range 32-74) were studied. All with HIV were receiving ART for median 48 months (7-227), HIV VL 1.5 copies/mL (<0.5–37), and CD4 378 cells/µl (135–752). At week 4 and 8 of therapy we observed significant increases in CD4 and CD8 counts, with a decline in CD19 B cells and no change in NK cells or HIV VL. A transient increase in KSHV VL was seen at week 4, not sustained at week 8: Abstract 4128. Table 1ParameterBaseline (cells/µl unless noted)Change to Week 4 (Med, range)PChange to Week 8 (Med, range)PCD31143 (525–2305)+264 (-419–1524)0.0028+210 (-496–1455)0.0020CD4429 (135–1171)+107 (-87–650)0.0009+86 (-37–491)0.0015CD8495 (259–1529)+108 (-271–915)0.0085+155 (-495–834)0.0046NK184 (28–557)+30 (-130–117)0.52+2 (-174–127)0.98CD19139 (9–322)-47 (-117–76)0.0039-79 (-169–62)<0.0001KSHV VL 0 copies/PBMC (0–8750)+23 (-92–5250)0.00980 (-92–20850)0.31Plasma HIV VL (infected pts)1.5 copies/mL (<0.5–37)+0.3 (-1.5–3.0)0.75+0.75 (0–28)0.13 In addition, at week 8 both CD4 and CD8 T cells showed significant increases in activation (CD38+, HLADR+ and DR+/38+) and decreases in senescence (CD57+). Both also showed a significant shift towards increased central memory (CM) and away from naive (N) and effector (E) phenotypes, with no change in effector memory (EM) cells: Abstract 4128. Table 2CD4 SubsetsBaseline (%) (med, range)Absolute Change in % at Week 8 (med, range)PRO- 27+ (N)32.6 (13.3–76.5)-6.6 (-35.8–21.6)0.002RO+ 27+ (CM)41.9 (13.6–63.6)+6.4 (-15.5–32.5)0.027RO+ 27- (EM)16.7 (4.6–31.7)+1.7 (-7.2–21.0)0.28RO- 27- (E)3.3 (0.4–14.3)-1.5 (-5.7–0.3)0.000438+34.5 (11.2–67.3)+4.3 (-13.0–19.4)0.024HLA DR+8.9 (3.3–25.0)+8.3 (0.7–19.5)<0.000138+ DR+2.5 (0.6–11.7)+2 (-1.0–8.1)<0.000157+6.3 (0.6–26.6)-1.34 (-16.2–7.6)0.034CD8 SubsetsRO- 27+ (N)21.0 (9.7–70.4)-5.1 (-13.7–14.3)0.019RO+ 27+ (CM)17.1 (2.5–37.9)+8.1 (-8.4–18.6)0.0047RO+ 27- (EM)18.4 (4.6–40.8)+1.0 (-9.4–44.9)0.35RO- 27- (E)31.8 (4.1-63.7)-6.1 (-47.3–22.5)0.0138+33.4 (8.3–66.0)+19.9 (-0.8–40.6)<0.0001HLA DR+19.6 (5.0–46.4)+11.6 (-4.7–32.1)0.000138+ DR+8.0 (0.4–33.3)+8.5 (0.1–22.6)<0.000157+30.8 (2.9–72.9)-11.0 (-28.5–6.1)<0.0001 There were no significant changes in Ki67 or PD-1 expression in either CD4 or CD8 cells. There was no significant difference between HIV infected and uninfected patient groups in the observed effects on any parameter including cell number and phenotype. Conclusions: Pomalidomide induced significant increases in the number of CD4 and CD8 T cells and the proportion of activated and central memory cells and decreased senescence in both HIV infected and uninfected subjects. Effects were not explained by alterations in HIV viremia. The transient early rise in KSHV VL may reflect reactivation of latent infection and enhance immune killing of KSHV infected cells. This analysis sheds light on possible mechanisms of IMID activity in viral-associated tumors. As the first study of immune modulation by IMIDs in vivo in people with HIV it also suggests exploration of IMIDs to augment immune responsiveness in HIV and other immunodeficiencies is warranted. Disclosures Polizzotto: Celgene Corporation: Research Funding. Off Label Use: Pomalidomide for Kaposi sarcoma. Uldrick:Celgene Corporation: Research Funding. Zeldis:Celgene Corporation: Employment, Equity Ownership, Patents & Royalties. Yarchoan:Celgene Corporation: Research Funding.