AJKD Atlas of Renal Pathology: Cytomegalovirus Infection

Intraepithelial Inclusions on Urinalysis Screening among COVID-19 Cases: Are they Covicytes?-A Hospital-Based Cohort Study with Narrative Review

Title

"Intraepithelial inclusions on urinalysis screening among COVID-19 cases: Are they Covicytes?-A hospital-based cohort study with narrative review."

Context

Coronavirus disease 2019 (COVID-19)-associated delayed acute kidney injury (AKI) is often reported in subsequent waves of the pandemic. Early intervention and regular follow-up influence the outcome and inhibit progression into chronic kidney disease (CKD). This is the first study to identify urinary cytomorphological abnormalities (Covicytes) and predict COVID-19-associated delayed AKI with a narrative review of the possible etiologies for intraepithelial inclusions.

Settings and Design

A hospital-based cohort study with a narrative review.

Material and Methods

Screening urinalysis to assess the cytomorphology of epithelial cells (ECs) and inclusions in Leishman and periodic acid-Schiff (PAS)-stained smears by two independent pathologists was performed in reverse transcriptase polymerase chain reaction (RT-PCR)-confirmed COVID-19 cases at a tertiary care center.

Statistical Analysis

Basic statistical tools were used for descriptive statistical analysis, and data were expressed in mean, proportion, and frequency.

Results

Cytomorphological abnormalities (48/188) were predominant among adult males. Leukocyturia (39/48) with positive nitrite test (28/39), high ECs (27/48) and squamous cell-to-tubular EC (SC:TEC) ratio, intraepithelial intracytoplasmic inclusions predominantly in TECs (Covicytes), and multiple well-visualized, perinuclear PAS-negative neutrophilic vacuoles (17/39) were found. The association with preexisting diabetes (31/48), hypertension (10/48), and disease severity was noted.

Conclusions

This study reported COVID-19-associated urinary cytomorphological abnormalities and interesting unique inclusions (Covicytes) that may be a result of underlying inflammatory changes, reactive hyperplasia, degenerative changes, or defective endocytosed vacuoles. The possible etiologies for renal inclusions were reviewed. We recommend compulsory baseline and follow-up urinary cytology screening for all COVID-19-suspected patients to detect and predict delayed AKI before clinical and biochemical manifestation during disease endemicity.

Pathological Approach to Kidney Allograft Infection

Infectious agents can pose a significant challenge in kidney transplantation, as they have the potential to cause direct infections in the transplanted kidney. These infections can lead to a decline in kidney function and reduce the longevity of the transplanted kidney. Common post-transplant allograft infections include bacterial pyelonephritis and the BK virus infection, while adenovirus, JC virus, and cytomegalovirus are less frequent but can also lead to significant allograft dysfunctions. The histopathological features of these infections are characterized by the infiltration of inflammatory cells in the kidney interstitial area and the presence of viral nuclear inclusions or cytopathic changes in the renal tubular epithelial cells. The confirmation of causative organisms can be achieved by immunohistochemical staining or the visualization of viral particles using electron microscopic examination. However, these methods typically require a longer turnaround time and are not readily available in developing countries, unlike standard hematoxylin-eosin staining. Notably, the differential diagnosis of interstitial inflammation in kidney allografts almost always includes T cell-mediated rejection, which has a different treatment approach than allograft infections. The aim of this review was to prompt clinicians to identify diverse pathological alterations as observed in kidney allograft biopsies, thereby facilitating further investigations and the management of suspected kidney allograft infections.

Tissue-resident memory T cells in renal autoimmune diseases

The discovery of tissue-resident memory T cells (T_RM cells) reinterpreted the potential of human tissue-specific immunity. Following T cell receptor (TCR) activation and clonal expansion, effector T cells migrate to peripheral tissues where they remain long-term and differentiate to T_RM cells after antigen clearance. This allows for prompt immunological responses upon antigen re-encounter. In addition to their protective properties in acute infections, recent studies have revealed that T_RM cells might lead to aggravation of autoimmune diseases, such as lupus nephritis (LN) and anti-neutrophil cytoplasmic antibody (ANCA)-associated glomerulonephritis (GN). These diseases present as proliferative and crescentic glomerulonephritis (cGN), which is a life-threatening condition leading to end-stage renal disease (ESRD) if left untreated. A better understanding of renal T_RM cells might lead to identifying new therapeutic targets for relapsing autoimmune diseases of the kidney. In this review, we summarize the current knowledge of renal T_RM cells and discuss their potential pathophysiological roles in renal autoimmune diseases.

Tissue-resident memory T cells in the kidney

The identification of tissue-resident memory T cells (T_RM cells) has significantly improved our understanding of immunity. In the last decade, studies have demonstrated that T_RM cells are induced after an acute T-cell response, remain in peripheral organs for several years, and contribute to both an efficient host defense and autoimmune disease. T_RM cells are found in the kidneys of healthy individuals and patients with various kidney diseases. A better understanding of these cells and their therapeutic targeting might provide new treatment options for infections, autoimmune diseases, graft rejection, and cancer. In this review, we address the definition, phenotype, and developmental mechanisms of T_RM cells. Then, we further discuss the current understanding of T_RM cells in kidney diseases, such as infection, autoimmune disease, cancer, and graft rejection after transplantation.