Rare presentation of kappa light chain proximal tubulopathy with fibrillar aggregates

Introduction/Objective Patients with dysproteinemias may show a spectrum of renal alterations due to organized deposits of excess immunoglobulins, including primary amyloidosis, myeloma cast nephropathy, monoclonal immunoglobulin deposition disease, and light chain proximal tubulopathy (LCPT). Among the least common is LCPT, which shows ultrastructural cytoplasmic light chain inclusions with crystalline morphology or rarely fibrillar aggregates. We present the case of a patient with LCPT with fibrillar aggregates that is the only such case registered in our large academic surgical pathology electronic database. Our aim is to increase understanding and recognition of this rare variant. Methods/Case Report A 73-year-old man presented with 540 mg/day proteinuria, serum creatinine 5.73 mg/dL, platelets 178,000/cc, and 20% plasma cells in his bone marrow biopsy specimen. Kidney needle biopsy cores examined by light, fluorescent and transmission electron microscopy (EM) showed kappa light chain cast nephropathy and kappa LCPT with fibrillary aggregates, the latter requiring unmasking of kappa epitopes using pronase-treated paraffin sections. Congo red stain was negative. By EM, proximal tubules contained intracellular bundles of tightly aggregated fibrils with mean fibril diameter of 7.7 +/- 1.6 nm. Individual bundles were variably shaped as round, oval, spicular or irregular blobs. Fibrils were not seen in glomeruli. Results (if a Case Study enter NA) NA Conclusion This rare presentation of LCPT with fibrillar aggregates reinforces the utility of renal biopsy diagnosis that includes careful ultrastructural examination of renal tubules. In the absence of EM, the unique fibrillar organization of these cytoplasmic light chain aggregates would otherwise go unrecognized.

The light chain of the L9 antibody is critical for binding circumsporozoite protein minor repeats and preventing malaria

L9 is a potent human monoclonal antibody (mAb) that preferentially binds two adjacent NVDP minor repeats and cross-reacts with NANP major repeats of the Plasmodium falciparum circumsporozoite protein (PfCSP) on malaria-infective sporozoites. Understanding this mAbs ontogeny and mechanisms of binding PfCSP to neutralize sporozoites will facilitate vaccine development. Here, we isolated mAbs clonally related to L9 and showed that this B-cell lineage has baseline NVDP affinity and evolves to acquire NANP reactivity. Pairing the L9 kappa light chain (L9k) with clonally-related heavy chains resulted in chimeric mAbs that cross-linked two NVDP, cross-reacted with NANP, and more potently neutralized sporozoites compared to their original light chain. Structural analyses revealed that chimeric mAbs bound the minor repeat motif in a type-1 beta-turn seen in other repeat-specific antibodies. These data highlight the importance of L9k in binding NVDP on PfCSP to neutralize SPZ and suggest that PfCSP-based immunogens might be improved by presenting 2 or more NVDP.

Association of kappa light chain restriction with peripheral neuropathy among patients with non-IgM monoclonal gammopathy of undetermined significance.

e20040 Background: Monoclonal gammopathy of undetermined significance (MGUS) can be associated with significant neurologic morbidity. Of non-IgM MGUS, types IgG and IgA are most commonly associated with peripheral neuropathy (PN). Methods: With IRB approval, we conducted a retrospective cohort study of consecutive patients with non-IgM type MGUS treated at our institution from 2014-2021. Other conditions potentially causing PN were excluded. Statistical analysis: Descriptive statistics were calculated to characterize the study population, and Relative Risk (RR) of PN was evaluated for selected patient, and disease, related factors. P < 0.05 was defined as statistically significant. Results: During the study period, 94 patients with non-IgM type MGUS were seen and comprised the study population. Twenty-two (23.4%) had evidence of PN. Median age was 74; 82% (18/22 ) were Caucasian; 73% (16/22) were women. 82% (18/22) patients had MGUS type IgG kappa or IgA kappa. We identified only 2 patients with each MGUS kappa light chain (LC) and MGUS IgG lambda. Median M-protein size was 0.11 g/dL, and median free LC value was 6.84 mg/L. Incidence/severity of kidney disease was similar in non-IgM MGUS patients with and without PN (p > 0.05). RR of PN was not found to be significantly different based on race or gender, although there appeared to be a tendency for women to be at higher risk compared to men (RR = 1.98, 95% CI = 0.85 to 4.60, p = 0.114.) Kappa LC restriction was strongly associated with PN (RR = 4.31, 95% CI = 1.58 to 11.78; p = 0.004). Electromyographic (EMG) studies identified 14 patients (64%) with distal symmetric axonal neuropathy (DSAN) and 8 patients (36%) with chronic inflammatory demyelinating polyneuropathy (CIDP). Clinically severe PN was identified in 11 (50%) patients; all were subsequently treated with IVIg therapy. Only 5/11 (45%) patients responded to IVIg, and the responses were only partial and transient. Conclusions: This is the first report, to our knowledge, of a significant association of kappa (as opposed to lambda) LC restriction with PN among patients with non-IgM type MGUS. Further investigation is warranted to explain this finding, elucidate pathophysiology and aid in developing more effective therapeutic options. Pending mechanistic characterization of this association, trials of contemporary agents used to treat other plasma cell disorders may be in order. Final statistical analysis, comparison to published series and significance will be presented.

Immunoglobulin-Storing Histiocytosis: A Case Based Systemic Review

Crystal-storing histiocytosis (CSH) is a rare event in disorders associated with monoclonal gammopathy and is mostly associated with the accumulation of immunoglobulins (Igs) in the cytoplasm of histiocytes. In this article, we present a case of a 75-year-old female with IgG kappa monoclonal gammopathy of undetermined significance (MGUS) and signs of a non-crystallized version of immunoglobulin-storing histiocytosis (IgSH) in a vertebra corpus. Furthermore, we performed a literature review based on all cases of storing histiocytosis identified by literature search between 1987 and 2020 and identified 140 cases in total. The median age at diagnosis was 60 years (range 18–91), with an equal sex distribution (51% men). The majority of the patients had an underlying neoplastic B-cell disorder, most often multiple myeloma (MM), MGUS, or lymphoplasmacytic lymphoma (LPL). The main affected organ systems or tissue sites were bone (n = 52), followed by head and neck (n = 31), kidney (n = 23), lung (n = 20), and gastrointestinal (GI)-tract (n = 18). IgG was the main immunoglobulin class involved, and most cases were associated with kappa light chain expression. We conclude that IgSH is a rare disease entity but should be considered with unusual findings in several organ systems associated with monoclonal gammopathy, especially with kappa light chain expression.

Atypical Nodular Pulmonary Kappa Light-Chain Deposition

We report a case of an incidental positron emission tomography avid right middle lobe lesion which was increasing in size. Due to concerns regarding malignancy, the patient underwent right middle lobectomy. Microscopic examination showed a 12 × 10 × 10 mm poorly circumscribed lesion composed of eosinophilic material. The material labelled strongly for kappa light chains; however, Congo red stain was only weakly positive and without “apple-green” positive birefringence under polarised light. Electron microscopy revealed fibrillar amyloid-like material. The features were those of kappa light-chain deposition.