Distinct serotypes of streptococcal M proteins mediate fibrinogen-dependent platelet activation and pro-inflammatory effects

Quantification of Adaptive Immune Responses Against Protein-Binding Interfaces in the Streptococcal M1 Protein

Bacterial or viral antigens can contain subdominant protein regions that elicit weak antibody responses upon vaccination or infection although there is accumulating evidence that antibody responses against subdominant regions can enhance the protective immune response. One proposed mechanism for subdominant protein regions is the binding of host proteins that prevent antibody production against epitopes hidden within the protein binding interfaces. Here, we used affinity purification combined with quantitative mass spectrometry (AP-MS) to examine the level of competition between antigen-specific antibodies and host-pathogen protein interaction networks using the M1 protein from Streptococcus pyogenes as a model system. As most humans have circulating antibodies against the M1 protein, we first used AP-MS to show that the M1 protein interspecies protein network formed with human plasma proteins is largely conserved in naïve mice. Immunizing mice with the M1 protein generated a time-dependent increase of anti-M1 antibodies. AP-MS analysis comparing the composition of the M1-plasma protein network from naïve and immunized mice showed significant enrichment of 292 IgG peptides associated with 56 IgG chains in the immune mice. Despite the significant increase of bound IgGs, the levels of interacting plasma proteins were not significantly reduced in the immune mice. The results indicate that the antigen-specific polyclonal IgG against the M1 protein primarily targets epitopes outside the other plasma protein binding interfaces. In conclusion, this study demonstrates that AP-MS is a promising strategy to determine the relationship between antigen-specific antibodies and host-pathogen interaction networks that could be used to define subdominant protein regions of relevance for vaccine development.

Streptococcal Bacteremia and Toxic Shock Syndrome: A Rare Etiology Requiring Prompt Diagnosis

Bullous impetigo leading to streptococcal toxic shock syndrome (STSS) immune activation and massive cytokine release is a rare condition. It has a significant mortality rate, which calls for quick diagnosis, early suspicion, and integrated treatment. Herein, we discuss the case of a 66-year-old man who underwent evaluation for leg swelling before quickly going into shock and experiencing respiratory failure, which necessitated invasive mechanical intubation. Streptococcus pyogenes was identified by blood culture, and STSS was identified. Recommended antibiotics, intravenous (IV) immunoglobulin, and fluids made up the treatment regimen. In this case, the streptococcal infection deteriorated very quickly, and there was a rare relationship with bullous impetigo, which led to shock and respiratory failure. This case sheds lights on the need of having an early suspicion of this syndrome when a diabetic patient develops a skin lesion. A prompt diagnosis is necessary.

Phenotypic Characterization of Acoustically Enriched Extracellular Vesicles from Pathogen-Activated Platelets

Extracellular vesicles (EVs) are derived from the membrane of platelets and released into the circulation upon activation or injury. Analogous to the parent cell, platelet-derived EVs play an important role in hemostasis and immune responses by transfer of bioactive cargo from the parent cells. Platelet activation and release of EVs increase in several pathological inflammatory diseases, such as sepsis. We have previously reported that the M1 protein released from the bacterial pathogen Streptococcus pyogenes directly mediates platelet activation. In this study, EVs were isolated from these pathogen-activated platelets using acoustic trapping, and their inflammation phenotype was characterized using quantitative mass spectrometry-based proteomics and cell-based models of inflammation. We determined that M1 protein mediated release of platelet-derived EVs that contained the M1 protein. The isolated EVs derived from pathogen-activated platelets contained a similar protein cargo to those from physiologically activated platelets (thrombin) and included platelet membrane proteins, granule proteins, cytoskeletal proteins, coagulation factors, and immune mediators. Immunomodulatory cargo, complement proteins, and IgG3 were significantly enriched in EVs isolated from M1 protein-stimulated platelets. Acoustically enriched EVs were functionally intact and exhibited pro-inflammatory effects on addition to blood, including platelet-neutrophil complex formation, neutrophil activation, and cytokine release. Collectively, our findings reveal novel aspects of pathogen-mediated platelet activation during invasive streptococcal infection.

Multienzyme deep learning models improve peptide de novo sequencing by mass spectrometry proteomics

Generating and analyzing overlapping peptides through multienzymatic digestion is an efficient procedure for de novo protein using from bottom-up mass spectrometry (MS). Despite improved instrumentation and software, de novo MS data analysis remains challenging. In recent years, deep learning models have represented a performance breakthrough. Incorporating that technology into de novo protein sequencing workflows require machine-learning models capable of handling highly diverse MS data. In this study, we analyzed the requirements for assembling such generalizable deep learning models by systemcally varying the composition and size of the training set. We assessed the generated models' performances using two test sets composed of peptides originating from the multienzyme digestion of samples from various species. The peptide recall values on the test sets showed that the deep learning models generated from a collection of highly N- and C-termini diverse peptides generalized 76% more over the termini-restricted ones. Moreover, expanding the training set's size by adding peptides from the multienzymatic digestion with five proteases of several species samples led to a 2-3 fold generalizability gain. Furthermore, we tested the applicability of these multienzyme deep learning (MEM) models by fully de novo sequencing the heavy and light monomeric chains of five commercial antibodies (mAbs). MEMs extracted over 10000 matching and overlapped peptides across six different proteases mAb samples, achieving a 100% sequence coverage for 8 of the ten polypeptide chains. We foretell that the MEMs' proven improvements to de novo analysis will positively impact several applications, such as analyzing samples of high complexity, unknown nature, or the peptidomics field.

Streptococcal Toxic Shock Syndrome: A Case Report

Streptococcal toxic shock syndrome is a serious complication of group A Streptococcus infection with a high mortality rate. Rapid detection, early intensive care support, and surgical management are paramount in treating these patients. We present a case of a 65-year-old male, with a documented medical history of hypertension, type 2 diabetes mellitus, and peripheral arterial disease. The patient was evaluated in the emergency department with a chief complaint of pain, swelling in his left leg, and fever. Physical examination showed tachycardia, hypotension, and clear inflammatory signs in the left leg. After initial clinical and laboratory evaluation, the patient was admitted with a diagnosis of cellulitis and urinary tract infection. He presented progressive worsening with multi-organ dysfunction, requiring vasopressor support, invasive mechanical ventilation, and renal replacement therapy. Streptococcus pyogenes was isolated in blood cultures, and a streptococcal toxic shock syndrome was considered. Appropriate antibiotic therapy, immunoglobulins, hemoperfusion, and corticosteroid therapy were administered, with clinical improvement. During hospitalization, there was a progressive improvement in the skin lesion. Once clinically stabilized the patient was discharged with follow-up. The case presented shows the rapid evolution of cutaneous streptococcal infection with multiorgan dysfunction. Although these types of infections have an associated high mortality rate, this patient survived. The use of immunoglobulin and hemoperfusion technique, in this case, might have contributed to this positive outcome. Therefore, we highlight the need for high suspicion of this syndrome, especially in diabetic patients presenting with skin lesions. Once the diagnosis is established, these infections require close surveillance and rapid and intensive treatment.