COVID-19 virus: the immune reaction to vaccines

The immune system is developed to preserve its hosts from an ever-expanding cluster of pathogenic microbes. The elimination of toxic substances, allergens, or any other harmful existences that come in, passing the mucosal surfaces, is as well the responsibility of this special system. Its ability to distinguish self (our bodies' functioning cells and tissues) from non-self is the key aspect to its ability to mobilize some reaction to an invasion initiated by the stranger substances listed above. To identify and kill unsafe microorganisms, the host applies both natural and versatile systems, our innate and adaptive immune systems. Vaccines are used to combat the current SARS-CoV-2 strain by utilizing immune system mechanisms, specifically the adaptive immune system. Vectored vaccines, protein vaccines, genetic vaccine, and monoclonal antibody for passive vaccination are among the vaccine platforms under consideration for SARS-CoV-2. Each vaccine has its own benefits and drawbacks. This paper is written to describe the three major forms of COVID-19 vaccines, as well as the unique mechanisms of elements of the immune system associated with the virus. © 2023 SPIE.

A Review of mRNA Vaccines with the Aid of Lipid Nanoparticles

This review article highlights the importance of messenger ribonucleic acid (mRNA) vaccines and how it has been developed to fight against various diseases such as, human immunodeficiency virus (HIV), rabies, cancer treatments, and coronavirus (Covid-19). During the past two years, covid-19 has become a worldwide pandemic, and the mRNA has played a major role in the manufacturing of its vaccine. We have highlighted the technology behind the development of mRNA vaccine, synthesis, and working of the lipid nanoparticles (LNPs). This mRNA vaccine produces a duplicate of a molecule that corresponds to a viral protein for producing an immune response, and these are given to us in a series of shots designed to protect us from developing a disease. The LNPs which carry the mRNA protein prevent the degradation of it and maintain more constant serum levels. In addition, this review article specifically mentions HIV, rabies, cancer, covid-19 and how these are important in the treatment of these diseases. This review article further highlights the mRNA vaccines for the survival of human beings against various deadly diseases in the near future. © 2023, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Delayed Urticaria- Angioedema After mRNA Vaccine in an Adolescent Patient: Case Report

Messenger RNA (mRNA) vaccines have long been suggested as encouraging candidates for widespread vaccination since they are manufactured rapidly and induce both humoral and cellular immune system components against pathogens. Available data on the efficacy and safety of these vaccines are relatively limited and the spectrum of skin reactions is still unclear. We would like to contribute to the literature by presenting a rare case with cutaneous reactions and discussing the skin complications of these kinds of vaccines. Our patient was a 17-year-old healthy female patient who applied to the pediatric emergency department with urticarial plaques that started from the legs and spread to the trunk nearly 80 hours after the second dose of the BioNTech-Pfizer COVID-19 vaccine was applied. The patient, whose skin lesions recurred more severely within 24 hours at home, and who noticed mild swelling in the fingers of the right hand and on the lip, was brought to the emergency service for the second time. Patients and physicians should be aware of the risk of delayed adverse skin reactions as well as the development of immediate hypersensitivity reactions such as urticaria and angioedema after administration of an mRNA COVID-19 vaccine.

Validation of an HPLC-CAD Method for Determination of Lipid Content in LNP-Encapsulated COVID-19 mRNA Vaccines.

Lipid nanoparticles (LNPs) are widely used as delivery systems for mRNA vaccines. The stability and bilayer fluidity of LNPs are determined by the properties and contents of the various lipids used in the formulation system, and the delivery efficiency of LNPs largely depends on the lipid composition. For the quality control of such vaccines, here we developed and validated an HPLC-CAD method to identify and determine the contents of four lipids in an LNP-encapsulated COVID-19 mRNA vaccine to support lipid analysis for the development of new drugs and vaccines.

Postural orthostatic tachycardia syndrome-like symptoms following COVID-19 vaccination: An overview of clinical literature.

BACKGROUND: Postural Orthostatic Tachycardia Syndrome (POTS) is a common condition affecting more than 170 people per 100,000 population. However, POTS following COVID-19 vaccination remains a rare reporting in the medical literature. OBJECTIVE: We, herein, summarize and highlight the evidence that has been reported regarding POTS-like symptoms following COVID-19 vaccination. METHODS: We conducted a literature search and summarized the findings in the form of a narrative commentary. All types of publications (case reports/series, original articles, letters to editors, brief communications etc.) in English language were included. RESULTS: Whilst the exact pathogenetic mechanism behind POTS is yet to elucidated, there has been increasing evidence pointing towards an autoimmune dysfunction. Females were found to be predominantly affected (72%) with age range from 17 years to 52 years. Additionally, it seems that POTS-like symptoms could be triggered after immunization with Pfizer- BioNTech, Moderna, and Oxford-AstraZeneca COVID-19 vaccines. The symptoms typically appear within the first week, depending upon previous exposure to the virus and presence of other systemic conditions. In some patients, the condition is self-resolving. However, in others, non-pharmacological interventions coupled with negative ionotropic medications can be used for symptomatic management of the patients. CONCLUSIONS: Timely diagnosis and proper treatment are quintessential for ensuring early alleviation (and in some cases complete resolution) of symptoms. Furthermore, there may be episodes of relapse. Overall prognosis of the new-onset POTS-like symptoms is difficult to predict based on current literature.

A Pharmacoepidemiological Study of Myocarditis and Pericarditis Following the First Dose of mRNA COVID-19 Vaccine in Europe.

This study assessed the myocarditis and pericarditis reporting rate of the first dose of mRNA COVID-19 vaccines in Europe. Myocarditis and pericarditis data pertinent to mRNA COVID-19 vaccines (1 January 2021-11 February 2022) from EudraVigilance database were combined with European Centre for Disease Prevention and Control (ECDC)'s vaccination tracker data. The reporting rate was expressed as events (occurring within 28 days of the first dose) per 1 million individuals vaccinated. An observed-to-expected (OE) analysis quantified excess risk for myocarditis or pericarditis following the first mRNA COVID-19 vaccination. The reporting rate of myocarditis per 1 million individuals vaccinated was 17.27 (95% CI, 16.34-18.26) for CX-024414 and 8.44 (95% CI, 8.18-8.70) for TOZINAMERAN; and of pericarditis, 9.76 (95% CI, 9.06-10.51) for CX-024414 and 5.79 (95% CI, 5.56-6.01) for TOZINAMERAN. Both vaccines produced a myocarditis standardized morbidity ratio (SMR) > 1, with the CX-024414 vaccine having a greater SMR than TOZINAMERAN. Regarding TOZINAMERAN, SMR for pericarditis was >1 when considering the lowest background incidence, but <1 when considering the highest background incidence. Our results suggest an excess risk of myocarditis following the first dose of the mRNA COVID-19 vaccine, but the relationship between pericarditis and the mRNA COVID-19 vaccine remains unclear.

Predominantly defective CD8+ T cell immunity to SARS-CoV-2 mRNA vaccination in lung transplant recipients.

BACKGROUND: Although mRNA vaccines have overall efficacy preventing morbidity/mortality from SARS-CoV-2 infection, immunocompromised persons remain at risk. Antibodies mostly prevent early symptomatic infection, but cellular immunity, particularly the virus-specific CD8+ T cell response, is protective against disease. Defects in T cell responses to vaccination have not been well characterized in immunocompromised hosts; persons with lung transplantation are particularly vulnerable to vaccine failure with severe illness. METHODS: Comparison groups included persons with lung transplantation and no history of COVID-19 (21 and 19 persons after initial mRNA vaccination and a third booster vaccination respectively), 8 lung transplantation participants recovered from COVID-19, and 22 non-immunocompromised healthy control individuals after initial mRNA vaccination (without history of COVID-19). Anti-spike T cell responses were assayed by stimulating peripheral blood mononuclear cells (PBMCs) with pooled small overlapping peptides spanning the SARS-CoV-2 spike protein, followed by intracellular cytokine staining (ICS) and flow cytometry for release of cytokines in response to stimulation, including negative controls (no peptide stimulation) and positive controls (phorbol myristate acetate [PMA] and ionomycin stimulation). To evaluate for low frequency memory responses, PBMCs were cultured in the presence of the mRNA-1273 vaccine for 14 days before this evaluation. RESULTS: Ionophore stimulation of PBMCs revealed a less inflammatory milieu in terms of interleukin (IL)-2, IL-4, and IL-10 profiling in lung transplantation individuals, reflecting the effect of immunosuppressive treatments. Similar to what we previously reported in healthy vaccinees, spike-specific responses in lung transplantation recipients were undetectable (< 0.01%) when tested 2 weeks after vaccination or later, but were detectable after in vitro culture of PBMCs with mRNA-1273 vaccine to enrich memory T cell responses. This was also seen in COVID-19-recovered lung transplantation recipients. Comparison of their enriched memory responses to controls revealed relatively similar CD4+ T cell memory, but markedly reduced CD8+ T cell memory both after primary vaccination or a booster dose. These responses were not correlated to age or time after transplantation. The vaccine-induced CD4+ and CD8+ responses correlated well in the healthy control group, but poorly in the transplantation groups. CONCLUSIONS: These results reveal a specific defect in CD8+ T cells, which have key roles both in transplanted organ rejection but also antiviral effector responses. Overcoming this defect will require strategies to enhance vaccine immunogenicity in immunocompromised persons.

Potentiating the Cross-Reactive IFN-γ T Cell and Polyfunctional T Cell Responses by Heterologous GX-19N DNA Booster in Mice Primed with Either a COVID-19 mRNA Vaccine or Inactivated Vaccine.

Waning vaccine-induced immunity, coupled with the emergence of SARS-CoV-2 variants, has inspired the widespread implementation of COVID-19 booster vaccinations. Here, we evaluated the potential of the GX-19N DNA vaccine as a heterologous booster to enhance the protective immune response to SARS-CoV-2 in mice primed with either an inactivated virus particle (VP) or an mRNA vaccine. We found that in the VP-primed condition, GX-19N enhanced the response of both vaccine-specific antibodies and cross-reactive T Cells to the SARS-CoV-2 variant of concern (VOC), compared to the homologous VP vaccine prime-boost. Under the mRNA-primed condition, GX-19N induced higher vaccine-induced T Cell responses but lower antibody responses than the homologous mRNA vaccine prime-boost. Furthermore, the heterologous GX-19N boost induced higher S-specific polyfunctional CD4+ and CD8+ T cell responses than the homologous VP or mRNA prime-boost vaccinations. Our results provide new insights into booster vaccination strategies for the management of novel COVID-19 variants.

Humoral and cellular immune response to SARS-CoV-2 mRNA BNT162b2 vaccine in pediatric kidney transplant recipients compared with dialysis patients and healthy children.

BACKGROUND: Compared with the general population, the immune response to COVID-19 mRNA vaccines is lower in adult kidney transplant recipients (KTRs). However, data is limited for pediatric KTRs. In this study, we aimed to assess humoral and cellular immune responses to the COVID-19 mRNA vaccine in pediatric KTRs. METHODS: This multicenter, prospective, case-control study included 63 KTRs (37 male, aged 12-21 years), 19 dialysis patients, and 19 controls. Humoral (anti-SARS-CoV2 IgG, neutralizing Ab (nAb)) and cellular (interferon-gamma release assay (IGRA)) immune responses were assessed at least one month after two doses of BNT162b2 mRNA vaccine. RESULTS: Among COVID-19 naïve KTRs (n = 46), 76.1% tested positive for anti-SARS-CoV-2 IgG, 54.3% for nAb, and 63% for IGRA. Serum levels of anti-SARS-CoV-2 IgG and nAb activity were significantly lower in KTRs compared to dialysis and control groups (p < 0.05 for all). Seropositivity in KTRs was independently associated with shorter transplant duration (p = 0.005), and higher eGFR (p = 0.007). IGRA titer was significantly lower than dialysis patients (p = 0.009). Twenty (43.4%) KTRs were positive for all immune parameters. Only four of 11 seronegative KTRs were IGRA-positive. COVID-19 recovered KTRs had significantly higher anti-SARS-CoV-2 IgG and nAb activity levels than COVID-19 naïve KTRs (p = 0.018 and p = 0.007, respectively). CONCLUSIONS: The humoral and cellular immune responses to SARS-CoV-2 mRNA BNT162b2 vaccine are lower in pediatric KTRs compared to dialysis patients. Further prospective studies are required to demonstrate the clinical efficacy of the mRNA vaccine in KTRs. This prospective study was registered in ClinicalTrials.gov (NCT05465863, registered retrospectively at 20.07.2022). A higher resolution version of the Graphical abstract is available as Supplementary information.

Long-term effects of Pfizer-BioNTech COVID-19 vaccinations on platelets.

There is a global concern about the safety of COVID-19 vaccines associated with platelet function. However, their long-term effects on overall platelet activity remain poorly understood. Here we address this problem by image-based single-cell profiling and temporal monitoring of circulating platelet aggregates in the blood of healthy human subjects, before and after they received multiple Pfizer-BioNTech (BNT162b2) vaccine doses over a time span of nearly 1 year. Results show no significant or persisting platelet aggregation trends following the vaccine doses, indicating that any effects of vaccinations on platelet turnover, platelet activation, platelet aggregation, and platelet-leukocyte interaction was insignificant.

Evaluation of Anti-Severe Acute Respiratory Syndrome Coronavirus 2 Antibody Levels in Coronavirus Disease Breakthrough Infection During Immunosuppressive Therapy in a Patient with Connective Tissue Disease-Related Interstitial Lung Disease.

Herein, we report the case of a 67-year-old man with severe coronavirus disease (COVID-19) pneumonia and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mRNA vaccine breakthrough infection during immunosuppressive therapy for connective tissue disease-related interstitial lung disease (CTD-ILD). The patient received glucocorticoids combined with tacrolimus (TAC) as maintenance therapy. His serum anti-SARS-CoV-2-IgG antibody levels were extremely low at the onset of COVID-19 pneumonia, even after the second dose of SARS-CoV-2 mRNA vaccine (BNT162b2). After treatment for COVID-19 pneumonia, the levels of anti-SARS-CoV-2-IgG antibodies increased. These results indicated a lack of the ability to produce neutralizing antibodies from immune cells despite the booster vaccination. Therefore, we suggest that advanced age patients with CTD-ILD receiving immunosuppressive therapy with polypharmacy require consistent personal protection, vaccination of close caregivers, increased awareness, and booster vaccination. Moreover, we recommend that TAC should be withdrawn for a while after vaccination under controlled conditions.

Possible case of polyarteritis nodosa with epididymitis following COVID-19 vaccination: A case report and review of the literature.

The global outbreak of coronavirus disease (COVID-19) caused by severe acute respiratory syndrome coronavirus type 2 has prompted the rapid spread and development of vaccines to prevent the spread of the disease. COVID-19 vaccine has demonstrated excellent efficacy in reducing morbidity and severity of the disease, and most adverse reactions are very minor. However, some patients have been reported to develop autoimmune diseases, such as rheumatoid arthritis, myocarditis, Guillain-Barre syndrome, and vasculitis, following COVID-19 vaccination. Herein, we present a case of polyarteritis nodosa with epididymitis following COVID-19 mRNA vaccination. The patient's initial symptoms were fever and testicular pain, and magnetic resonance imaging showed epididymitis. He was diagnosed as having polyarteritis nodosa with epididymitis and treated with high-dose prednisolone, with a good clinical outcome.

IgA Vasculitis Following COVID-19 Vaccination.

IgA vasculitis is generally triggered by infectious causes, but it has also been reported after immunization with various vaccines. Herein, we report two cases of IgA vasculitis after receiving the first or second dose of the Pfizer-BioNTech BNT16B2b2 mRNA vaccine. Two men, aged 22 and 30 years, developed palpable purpura on the extremities and arthritis. One patient also complained of fever and gastrointestinal symptoms. Laboratory findings revealed mild leukocytosis and slightly elevated C-reactive protein level, although platelet count and coagulation profile were within normal levels in both cases. Proteinuria and microhematuria were seen in one patient. Skin biopsies were performed in both patients and revealed leukocytoclastic vasculitis. The deposit of IgA and C3 was shown on immunofluorescence studies in one patient. Both patients were diagnosed with IgA vasculitis and treated with prednisolone, and their symptoms resolved within 1 week after initiation of treatment. The COVID-19 mRNA vaccine could trigger IgA vasculitis; however, a coincidence cannot be ruled out.

SARS-CoV-2 Breakthrough Infections According to the Immune Response Elicited after mRNA Third Dose Vaccination in COVID-19-Naïve Hospital Personnel.

BACKGROUND: Vaccine-induced SARS-CoV-2-anti-spike antibody (anti-S/RBD) titers are often used as a marker of immune protection and to anticipate the risk of breakthrough infections, although no clear cut-off is available. We describe the incidence of SARS-CoV-2 vaccine breakthrough infections in COVID-19-free personnel of our hospital, according to B- and T-cell immune response elicited one month after mRNA third dose vaccination. METHODS: The study included 487 individuals for whom data on anti-S/RBD were available. Neutralizing antibody titers (nAbsT) against the ancestral Whuan SARS-CoV-2, and the BA.1 Omicron variant, and SARS-CoV-2 T-cell specific response were measured in subsets of 197 (40.5%), 159 (32.6%), and 127 (26.1%) individuals, respectively. RESULTS: On a total of 92,063 days of observation, 204 participants (42%) had SARS-CoV-2 infection. No significant differences in the probability of SARS-CoV-2 infection for different levels of anti-S/RBD, nAbsT, Omicron nAbsT, or SARS-CoV-2 T cell specific response, and no protective thresholds for infection were found. CONCLUSIONS: Routine testing for vaccine-induced humoral immune response to SARS-CoV-2 is not recommended if measured as parameters of 'protective immunity' from SARS-CoV-2 after vaccination. Whether these findings apply to new Omicron-specific bivalent vaccines is going to be evaluated.

Functional CVIDs phenotype clusters identified by the integration of immune parameters after BNT162b2 boosters.

Introduction: Assessing the response to vaccinations is one of the diagnostic criteria for Common Variable Immune Deficiencies (CVIDs). Vaccination against SARS-CoV-2 offered the unique opportunity to analyze the immune response to a novel antigen. We identify four CVIDs phenotype clusters by the integration of immune parameters after BTN162b2 boosters. Methods: We performed a longitudinal study on 47 CVIDs patients who received the 3rd and 4th vaccine dose of the BNT162b2 vaccine measuring the generation of immunological memory. We analyzed specific and neutralizing antibodies, spike-specific memory B cells, and functional T cells. Results: We found that, depending on the readout of vaccine efficacy, the frequency of responders changes. Although 63.8% of the patients have specific antibodies in the serum, only 30% have high-affinity specific memory B cells and generate recall responses. Discussion: Thanks to the integration of our data, we identified four functional groups of CVIDs patients with different B cell phenotypes, T cell functions, and clinical diseases. The presence of antibodies alone is not sufficient to demonstrate the establishment of immune memory and the measurement of the in-vivo response to vaccination distinguishes patients with different immunological defects and clinical diseases.

Longitudinal Assessment of Left Ventricular Function in Patients with Myopericarditis After mRNA COVID-19 Vaccination.

BACKGROUND: Multiple reports have described myopericarditis following mRNA COVID-19 vaccination. However, data on the persistence of subclinical myocardial injury assessed by left ventricular (LV) longitudinal strain (LVLS) is limited. OBJECTIVES: Our aim was to assess LV function longitudinally in our cohort of COVID-19 vaccine-related myopericarditis using ejection fraction (EF), fractional shortening (FS), LVLS, and diastolic parameters. METHODS: Retrospective, single-center review of demographic, laboratory, and management data was performed on 20 patients meeting diagnostic criteria for myopericarditis after mRNA COVID-19 vaccination. Echocardiographic images were obtained on initial presentation (time 0), at a median of 12 days (7.5, 18.5; time 1), and at a median of 44 days (29.5, 83.5; time 2). FS was calculated by M-mode, EF by 5/6 area-length methods, LVLS by utilization of TOMTEC software, and diastolic function by tissue Doppler. All parameters were compared across pairs of these time points using Wilcoxon signed-rank test. RESULTS: Our cohort consisted predominantly of adolescent males (85%) with mild presentation of myopericarditis. The median EF was 61.6% (54.6, 68.0), 63.8% (60.7, 68.3), 61.4% (60.1, 64.6) at times 0, 1, and 2, respectively. Upon initial presentation, 47% of our cohort had LVLS < -18%. The median LVLS was -18.6% (-16.9, -21.0) at time 0, -21.2% at time 1 (-19.4, -23.5) (p = 0.004) and -20.8% (-18.7, -21.7) at time 2 (p = 0.004, as compared to time 0). CONCLUSIONS: Though many of our patients had abnormal strain during acute illness, LVLS improved longitudinally, indicating myocardial recovery. LVLS can be used as marker of subclinical myocardial injury and risk stratification in this population.

SARS-CoV-2 bivalent mRNA vaccine with broad protection against variants of concern.

Introduction: The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron variant has rapidly spread around the globe. With a substantial number of mutations in its Spike protein, the SARS-CoV-2 Omicron variant is prone to immune evasion and led to the reduced efficacy of approved vaccines. Thus, emerging variants have brought new challenges to the prevention of COVID-19 and updated vaccines are urgently needed to provide better protection against the Omicron variant or other highly mutated variants. Materials and methods: Here, we developed a novel bivalent mRNA vaccine, RBMRNA-405, comprising a 1:1 mix of mRNAs encoding both Delta-derived and Omicron-derived Spike proteins. We evaluated the immunogenicity of RBMRNA-405 in BALB/c mice and compared the antibody response and prophylactic efficacy induced by monovalent Delta or Omicron-specific vaccine with the bivalent RBMRNA-405 vaccine in the SARSCoV-2 variant challenge. Results: Results showed that the RBMRNA-405 vaccine could generate broader neutralizing antibody responses against both Wuhan-Hu-1 and other SARS-CoV-2 variants, including Delta, Omicron, Alpha, Beta, and Gamma. RBMRNA-405 efficiently blocked infectious viral replication and lung injury in both Omicron- and Delta-challenged K18-ACE2 mice. Conclusion: Our data suggest that RBMRNA-405 is a promising bivalent SARS-CoV-2 vaccine with broad-spectrum efficacy for further clinical development.

Long-term follow-up of cardiac magnetic resonance imaging in myocarditis following messenger ribonucleic acid COVID-19 vaccination: a case report.

Background: Presently, the association between myocarditis and messenger ribonucleic acid (mRNA) COVID-19 vaccination is well established. From the most current data, cases of myocarditis following COVID-19 vaccination seem to be mild with fast clinical recovery. Nevertheless, the complete resolution of the inflammatory process is still unclear. Case summary: We report the case of a 13-year-old boy who developed chest pain following the second dose of the Pfizer-BioNTech COVID-19 vaccine with long-term follow-up of cardiac magnetic resonance (CMR) imaging. An electrocardiogram (ECG) revealed progressively ST-segment elevation on the 2nd day of admission with a rapid improvement within 3 hours where only mild ST-segment elevation remained. The peak level of high-sensitivity cardiac troponin T was 1546 ng/L with rapid reduction. Echocardiogram revealed depressed left ventricular septal wall motion. CMR mapping techniques showed myocardial oedema with an increase in native T1 and extracellular volume (ECV). On the other hand, T1-weighted and T2-weighted images and late gadolinium enhancement (LGE) did not detect inflammation. The patient's symptoms were relieved by oral ibuprofen. After 2 weeks, ECG and echocardiogram were unremarkable. However, the inflammation process was still present based on the CMR by mapping technique. During the 6-month follow-up, CMR returned to normal. Discussion: In our case, the subtle myocardial inflammation was diagnosed by mapping technique with only a T1-based marker according to the updated Lake Louise Criteria and the inflammation of the myocardium returned to normal within 6 months after the onset of the disease. Further follow-up and larger studies are needed to determine the complete resolution of the disease.

Clinicopathological Characteristics of Autoimmune-Like Hepatitis Induced by COVID-19 mRNA Vaccine (Pfizer-BioNTech, BNT162b2): A Case Report and Literature Review.

Widespread use of vaccinations worldwide in the coronavirus disease (COVID-19) pandemic has resulted in various side effects. Here, we presented a 27-year-old man with autoimmune-like hepatitis after the first dose of the BNT162b2 (mRNA) COVID-19 vaccine and reviewed previous reports. He presented with sweating, febrile sensations, and general weakness. He did not have any medical histories. Although he was treated with biphenyl dimethyl dicarboxylate and ursodeoxycholic acid, the elevated liver enzyme levels persisted for 2 months. Liver biopsy demonstrated portal inflammation with rosette formation, interface hepatitis, and infiltration of lymphocytes, histiocytes, plasma cells, and eosinophils. Especially, centrilobular edema and necrosis were found. The symptoms and liver enzymes improved with prednisolone treatment. If persistently elevated liver enzymes are found after COVID-19 mRNA vaccination, the possibility of autoimmune-like hepatitis induced by the vaccine should be considered and a careful pathologic evaluation is required.

Memory B cell differentiation from germinal centers.

Establishment of humoral immune memory depends on two layers of defense: pre-existing antibodies secreted by long-lived plasma cells; and the antibodies produced by antigen-reactivated memory B cells. Memory B cells can now be considered as a second layer of defense upon re-infection by variant pathogens that have not been cleared by the long-lived plasma cell-mediated defense. Affinity-matured memory B cells are derived from the germinal center (GC) reaction, but the selection mechanism of GC B cells into the memory compartment is still incompletely understood. Recent studies have revealed the critical determinants of cellular and molecular factors for memory B cell differentiation from the GC reaction. In addition, the contribution of antibody-mediated feedback regulation to B cell selection, as exemplified by the B cell response upon COVID-19 mRNA vaccination, has now garnered considerable attention, which may provide valuable implications for future vaccine design.