Granzyme K drives a newly-intentified pathway of complement activation.

Granzymes are a family of serine proteases mainly expressed by CD8+ T cells, natural killer cells, and innate-like lymphocytes1,2. Although their major role is thought to be the induction of cell death in virally infected and tumor cells, accumulating evidence suggests some granzymes can regulate inflammation by acting on extracellular substrates2. Recently, we found that the majority of tissue CD8+ T cells in rheumatoid arthritis (RA) synovium, inflammatory bowel disease and other inflamed organs express granzyme K (GZMK)3, a tryptase-like protease with poorly defined function. Here, we show that GZMK can activate the complement cascade by cleaving C2 and C4. The nascent C4b and C2a fragments form a C3 convertase that cleaves C3, allowing further assembly of a C5 convertase that cleaves C5. The resulting convertases trigger every major event in the complement cascade, generating the anaphylatoxins C3a and C5a, the opsonins C4b and C3b, and the membrane attack complex. In RA synovium, GZMK is enriched in areas with abundant complement activation, and fibroblasts are the major producers of complement C2, C3, and C4 that serve as targets for GZMK-mediated complement activation. Our findings describe a previously unidentified pathway of complement activation that is entirely driven by lymphocyte-derived GZMK and proceeds independently of the classical, lectin, or alternative pathways. Given the widespread abundance of GZMK-expressing T cells in tissues in chronic inflammatory diseases and infection, GZMK-mediated complement activation is likely to be an important contributor to tissue inflammation in multiple disease contexts.

Plasmodium falciparum-Induced Autoimmune Hemolytic Anemia in a Pregnant Patient with Sickle Cell Disease.

BACKGROUND Sickle cell disease (SCD) is an autosomal recessive hereditary condition characterized by chronic hemolytic anemia and painful vaso-occlusive episodes. Homozygous sickle cell patients are at increased risk of morbidity and mortality from malaria. Autoimmune hemolytic anemia (AIHA) secondary to, or in the setting of, malarial infection is rare. In our case, the concurrence of Plasmodium falciparum malarial parasitemia and AIHA led to severe hemolytic anemia with an extensive packed red blood cell transfusion requirement. The patient's underlying SCD also contributed to the severity of the anemia and persistence of the malarial infection. CASE REPORT We report the case of a 29-year-old woman in the second trimester of pregnancy, with a history of SCD, who presented with severe anemia beyond her typical baseline in the setting of P. falciparum malaria. Hemolysis markers, including lactate dehydrogenase and bilirubin, were elevated. Direct Coombs testing was positive for IgG and C3 antibodies. Treatment with antimalarial agents and steroids led to clinical improvement and eventual clearance of the parasitemia. CONCLUSIONS Our patient's clinical course was most compatible with P. falciparum malaria-induced AIHA. Although she received a short course of steroids, it was treatment and clearance of the parasitemia that led to resolution of the hemolysis and a return to baseline hemoglobin levels. While the exact mechanism of AIHA in malaria is not well characterized, several unique mechanisms have been proposed and should be considered in cases of P. falciparum malaria manifesting with particularly severe hemolytic anemia.

Granzyme K+ CD8 T cells form a core population in inflamed human tissue.

T cell-derived pro-inflammatory cytokines are a major driver of rheumatoid arthritis (RA) pathogenesis. Although these cytokines have traditionally been attributed to CD4 T cells, we have found that CD8 T cells are notably abundant in synovium and make more interferon (IFN)-γ and nearly as much tumor necrosis factor (TNF) as their CD4 T cell counterparts. Furthermore, using unbiased high-dimensional single-cell RNA-seq and flow cytometric data, we found that the vast majority of synovial tissue and synovial fluid CD8 T cells belong to an effector CD8 T cell population characterized by high expression of granzyme K (GzmK) and low expression of granzyme B (GzmB) and perforin. Functional experiments demonstrate that these GzmK+ GzmB+ CD8 T cells are major cytokine producers with low cytotoxic potential. Using T cell receptor repertoire data, we found that CD8 GzmK+ GzmB+ T cells are clonally expanded in synovial tissues and maintain their granzyme expression and overall cell state in blood, suggesting that they are enriched in tissue but also circulate. Using GzmK and GzmB signatures, we found that GzmK-expressing CD8 T cells were also the major CD8 T cell population in the gut, kidney, and coronavirus disease 2019 (COVID-19) bronchoalveolar lavage fluid, suggesting that they form a core population of tissue-associated T cells across diseases and human tissues. We term this population tissue-enriched expressing GzmK or TteK CD8 cells. Armed to produce cytokines in response to both antigen-dependent and antigen-independent stimuli, CD8 TteK cells have the potential to drive inflammation.

Direct oral anticoagulants versus warfarin in patients with single antibody-positive anti-phospholipid syndrome.

BACKGROUND: The role of direct oral anticoagulants (DOACs) among patients with antiphospholipid syndrome (APLS) remains unclear. Warfarin has been shown to be superior to DOACs among high-risk APLS patients (particularly those with triple-positive APLS). However, it remains unknown whether DOACs may be appropriate for lower-risk patients such as those with single-positive APLS. METHODS: We conducted a retrospective study comparing the risk of recurrent thrombosis among single-positive APLS patients treated with DOACs (apixaban or rivaroxaban), and those treated with warfarin. RESULTS: One-hundred-forty-three single-positive APLS patients, newly started on anticoagulation following a first thrombotic event, were included. Median follow-up was 54 months (IQR 29-73 months). Ninety-one patients (64%) received warfarin and 52 patients (36%) received a DOAC. Six patients (6.6%) who received warfarin experienced a recurrent thrombotic event compared with 3 of 52 (5.8%) patients who received a DOAC (p = .845). There was no difference in event-free survival between groups (HR DOAC:Warfarin = 0.952, 95% CI 0.232 - 3.908). Major bleeding was similar in both groups. CONCLUSIONS: These findings suggest that DOACs may be a safe and effective option for patients with single-positive APLS. Prospective studies are needed to confirm these findings.

Clip ligation of contralateral P1 aneurysm: extending the working depth of microsurgery along the skull base.

Clip ligation of posterior circulation aneurysms can be challenging because of limited operative working space and angles. Certain proximal posterior cerebral (P1) aneurysms are especially challenging because of their locations within the lateral anterior interpeduncular fossa. We present a 52-year-old woman who had previously undergone coil embolization of a ruptured right-sided posterior communicating artery aneurysm. She also had two other small aneurysms (left posterior communicating artery and right P1 aneurysms). She underwent clip ligation of the latter two unruptured aneurysms through a left-sided pterional craniotomy. The microsurgical techniques to clip ligate a contralateral P1 aneurysm are discussed in the video. The video can be found here: http://youtu.be/YBE7FcFGlpQ .