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HKeyBio Industry Commentary
Top Five Rare Immune Mediated Diseases
Autoimmune Top 5 Series | Mechanisms Clinical Features and Therapeutic Directions
Originally published in Chinese on March 17, 2026. The scientific corrections in this edition use evidence available by that date.
HKeyBio’s take. Autoimmune disease encompasses more than a hundred described conditions. Many rare conditions remain underrecognized because they occur infrequently and are unfamiliar in routine clinical practice. This article reviews five representative rare immune-mediated diseases to support greater awareness of their mechanisms, clinical features, and therapeutic development.
Table 1. Five rare immune diseases and therapeutic targets.
No. | Condition | Estimated per 100,000 | Highlighted Targets |
1 | Autoimmune pancreatitis (AIP) | 0.8–2.2 | CD19, BAFF, PD-1 |
2 | Autoimmune encephalitis (AE) | 0.1–0.5 | CD19, BAFF |
3 | Cryoglobulinemia (CG) | 0.1–1 | CD19, BAFF, C5 |
4 | Mixed connective tissue disease (MCTD) | 0.5–1 | Type I interferon, IL-6, JAK |
5 | Adult-onset Still’s disease (AOSD) | 0.16–0.4 | IL-1β, IL-6, JAK |
Autoimmune pancreatitis (AIP) is a rare form of chronic pancreatic inflammation characterized by inflammatory infiltration and fibrosis. The estimated incidence is 0.8–2.2 cases per 100,000 and a contribution of 2–6% of chronic pancreatitis cases; these should be treated as study-dependent estimates, rather than a verified global incidence. Type 1 AIP is a characteristic organ manifestation of immunoglobulin G4-related disease (IgG4-RD). Type 2 AIP is a distinct condition and should not be classified as IgG4-RD. [1]
Immunopathogenesis.
Disrupted immune tolerance and abnormal activation of CD4+ and CD8+ T cells, B cells, and plasma cells contribute to pancreatic inflammation. Type 1 disease is associated with lymphoplasmacytic infiltration, storiform fibrosis, and obliterative phlebitis, which can lead to pancreatic enlargement, ductal narrowing, and impaired function. Elevated IgG4 and IgG4-positive plasma cells are important disease features, but do not establish that IgG4 antibodies directly cause all tissue damage. [1]
Clinical features and management.
Type 1 AIP often presents with painless obstructive jaundice rather than the severe pain typical of acute pancreatitis, and may be mistaken for pancreatic cancer. Weight loss, fatigue, diabetes, abdominal pain, and bloating may also occur. Extrapancreatic disease can involve the bile ducts, lacrimal and salivary glands, kidneys, lungs, and retroperitoneum, including sclerosing cholangitis and retroperitoneal fibrosis. Type 2 AIP more often presents with acute pancreatitis. [1]
Treatment aims to induce and maintain remission. Glucocorticoids such as prednisone are commonly used for induction, with rapid improvement in pancreatic swelling and jaundice in many patients. Steroid-dependent or relapsing disease may require steroid-sparing treatment. Agents include azathioprine, mycophenolate mofetil, and cyclophosphamide, although their evidence and suitability differ and they should not be treated as interchangeable routine choices. Rituximab, an anti-CD20 antibody, is an alternative induction or steroid-sparing option in selected relapsing or refractory type 1 AIP/IgG4-RD. [1]
Therapeutic development.
Research is pursuing more selective control of B cells, plasma cells, and T cells to reduce steroid dependence and relapse and enable more individualized treatment. CD19-directed therapy targets CD19-expressing B-lineage cells, including some plasmablasts and plasma cells, rather than all plasma cells. Inebilizumab was approved in the United States for adults with IgG4-RD on April 3, 2025; this broader indication should be distinguished from evidence generated specifically in AIP. [6]
Other ideas include T-cell modulation or depletion, small-molecule immunomodulation, and approaches related to antibodies against lactoferrin or carbonic anhydrase II. These antibodies are not validated disease-specific therapeutic targets, and AIP-specific clinical evidence for the proposed T-cell and antibody-specific strategies requires confirmation.
Figure 1. Proposed mechanisms of immune-mediated pancreatic injury. Supplied figure from Gallo et al. [1], Figure 1, © The Author(s) 2024; source license CC BY-NC 4.0. The image distinguishes type 1 and type 2 AIP and uses “AIP-3” for checkpoint inhibitor-associated pancreatic injury, a proposed designation rather than a universally accepted third AIP subtype.
Autoimmune encephalitis (AE) is a heterogeneous group of immune-mediated inflammatory disorders affecting the central nervous system. Its frequency depends on the subtype, population, and diagnostic period. The approximate incidence is 0.1–0.5 per 100,000. A population-based study in Olmsted County, Minnesota, reported an incidence of 0.8 per 100,000 person-years over 1995–2015. [7]
Mechanisms and presentation.
Anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis is a prominent antibody-defined subtype, particularly in children, young adults, and women. Other subtypes involve leucine-rich glioma-inactivated protein 1 (LGI1), contactin-associated protein-like 2 (CASPR2), gamma-aminobutyric acid (GABA) receptors, or other neuronal antigens; their age and sex distributions differ. Neuronal-surface autoantibodies can alter receptor trafficking and function, synaptic transmission, and neuronal excitability. NMDAR antibodies, for example, can promote receptor clustering and internalization, causing synaptic dysfunction. These mechanisms should not be reduced to a uniform process of inflammatory edema or irreversible neuronal injury. [2,8]
Typical features include psychiatric or behavioral changes, seizures, altered consciousness, movement disorders, sleep disturbances, and autonomic dysfunction. Some cases are tumor-associated, including anti-NMDAR encephalitis associated with ovarian teratoma, and belong to the spectrum of paraneoplastic autoimmunity.
Management and therapeutic development.
First-line immunotherapy commonly includes corticosteroids and intravenous immunoglobulin (IVIG), with plasma exchange also used according to the clinical situation. Rituximab or cyclophosphamide may be used when escalation is needed. Screening for an associated tumor and its removal or treatment are essential when relevant. [8]
Development is exploring B-cell and plasma-cell targeting and selective modulation of inflammatory pathways. CD19, BAFF/APRIL, complement, and approaches intended to neutralize or remove pathogenic autoantibodies, including monoclonal antibodies, bispecific formats, and small-molecule immunomodulators. Evidence and maturity differ substantially across these approaches; the list does not imply that every mechanism has an established AE clinical program. A 2025 publication describes the Phase 2b ExTINGUISH trial of inebilizumab in NMDAR encephalitis, providing a concrete example of clinical evaluation of CD19 targeting. [9]
Translational work on antibody detection, rapid diagnosis, and individualized immune treatment aims to improve recovery in severe disease, reduce long-term sequelae, and lower relapse risk.
Figure 2. Antibody-mediated NMDAR clustering and endocytosis in AE. Supplied illustration from Wang et al. [2]. The diagram contrasts physiological signaling with antibody-associated receptor downregulation and synaptic dysfunction; mAb5F6 and mAb2G7 are the antibodies illustrated in the original study. The source is licensed under CC BY-NC-ND 4.0.
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Cryoglobulinemia (CG) is the presence of immunoglobulins that precipitate at low temperatures and redissolve on warming. It is not uniformly an autoimmune systemic vasculitis. Type I disease is usually associated with a monoclonal B-cell or plasma-cell disorder and can cause an occlusive vasculopathy. Mixed cryoglobulinemia, types II and III, more commonly causes immune-complex-mediated small-vessel vasculitis and may accompany hepatitis C or B, autoimmune disease, or lymphoproliferative disorders. Cases without an identifiable cause also occur. The estimated incidence is 0.1–1 per 100,000 without a consistently defined epidemiological basis. [3,10]
Pathogenesis and clinical features.
Abnormal B-cell or plasma-cell populations produce monoclonal or mixed cryoglobulins. In type I disease, cryoglobulin aggregates can obstruct small vessels and cause ischemia. In mixed disease, cryoglobulin-containing immune complexes deposit in vessels and activate complement, with complement consumption and inflammatory mediator release contributing to tissue damage. The relative contributions of occlusion and immune-complex inflammation differ between subtypes. [3]
The classic triad of cryoglobulinemic vasculitis is palpable purpura, arthralgia, and weakness. Other manifestations include Raynaud phenomenon, skin ulcers, peripheral neuropathy, glomerulonephritis, abdominal pain, hepatosplenomegaly, and lymphadenopathy. Disease occurs across adult age groups. Severe cases can involve renal failure, bleeding, and serious infection, the latter also influenced by comorbidity and immunosuppressive treatment.
Management and therapeutic development.
Management first addresses the underlying cause, such as hepatitis infection or lymphoma, and includes keeping warm and avoiding cold exposure. For clinically significant mixed cryoglobulinemic vasculitis, glucocorticoids and rituximab are important options according to severity; rituximab is not limited to rescue after all conventional therapies fail. Plasma exchange can rapidly remove circulating cryoglobulins in selected life-threatening presentations. Cyclophosphamide or azathioprine may be used in selected settings. Hydroxychloroquine may also address an associated autoimmune condition but should not be described as a universal first-line treatment for cryoglobulinemic vasculitis. [10]
Development interests include B-cell activation, plasma-cell regulation, complement inhibition, and cytokine blockade. BAFF/APRIL, CD19, C5, abnormal B-cell clones, and immune-complex formation are potential directions. Their disease-specific evidence ranges from mechanistic rationale to early investigation and should be confirmed for each program, rather than implying a uniformly established clinical pipeline. The goals are fewer relapses, less organ injury, better long-term outcomes, and additional options for patients inadequately controlled by existing treatment.
Figure 3. Different mechanisms of type I and mixed cryoglobulinemia. Supplied illustration attributed to Cacoub et al. [3]. Type I cryoglobulin aggregates are contrasted with immune-complex formation and complement-associated vasculitis in types II and III.
Mixed connective tissue disease (MCTD) combines features of systemic lupus erythematosus, systemic sclerosis, inflammatory myopathies including polymyositis and dermatomyositis, and rheumatoid arthritis, with characteristic high-titer anti-U1 ribonucleoprotein (U1-RNP) antibodies. It particularly affects young and middle-aged women. The estimated incidence is 0.5–1 per 100,000, but estimates depend on classification and population: a Norwegian study reported adult-onset incidence of 0.21 per 100,000 per year and prevalence of 3.8 per 100,000. [4,11]
Disease biology and manifestations.
Pathogenesis is incompletely understood. Genetic susceptibility and environmental triggers intersect with B-cell activation, anti-U1-RNP responses, immune-complex biology, T-cell imbalance, type I interferon activation, and profibrotic pathways. These processes are implicated in multisystem inflammation involving vessels, skin, joints, lungs, and other organs, but direct antibody deposition should not be presented as a proven uniform cause of every manifestation. [4]
Core features include Raynaud phenomenon, swollen fingers, polyarthralgia or arthritis, myositis, esophageal dysmotility, and interstitial lung disease. Renal involvement is generally less prominent than in lupus, although it can occur. Fever, fatigue, serositis, and pulmonary arterial hypertension may also develop; pulmonary vascular and interstitial disease can substantially affect quality of life and long-term prognosis.
Management and development opportunities.
Treatment is guided by symptoms and organ involvement. Nonsteroidal anti-inflammatory drugs (NSAIDs), hydroxychloroquine, and calcium-channel blockers for Raynaud symptoms may be used for milder manifestations. More active or severe disease may require glucocorticoids with agents such as methotrexate, mycophenolate mofetil, or cyclophosphamide. Interstitial lung disease and pulmonary arterial hypertension require organ-specific management; rituximab may be considered in selected refractory or relapsing cases.
Research directions include type I interferon, BAFF, IL-6, and JAK signaling, together with antifibrotic, vascular, and pulmonary hypertension treatment strategies and combinations. Their relevance should be assessed against the organ phenotype and the population actually studied: evidence from other connective tissue diseases or mixed cohorts does not by itself establish MCTD-specific efficacy. The goals remain reduced steroid dependence, better organ protection, fewer relapses, and more precise individualized treatment.
Figure 4. Conceptual model of RNP autoantigen-driven autoimmunity in MCTD. Supplied illustration attributed to Hoffman and Maldonado [4]. This is a mechanistic model, not documentation of a fully validated preclinical disease model. No republication authorization is established by the supplied file.
Adult-onset Still’s disease (AOSD) is a rare systemic autoinflammatory disorder of incompletely understood cause, characterized by fever, rash, and arthritis. It often affects young adults, although onset can occur at other ages. The estimated incidence is 0.16–0.4 per 100,000. [5]
Innate immune activation and presentation.
Genetic susceptibility and abnormal innate immune activation are implicated. Macrophages and neutrophils, IL-1β, IL-6, IL-18, and pathways involving NF-κB and the NLRP3 inflammasome contribute to systemic hyperinflammation. Typical findings include spiking fever, a transient salmon-colored rash, often symmetric inflammatory polyarthritis, sore throat, hepatosplenomegaly or lymphadenopathy, leukocytosis, and marked hyperferritinemia. Macrophage activation syndrome (MAS) and disseminated intravascular coagulation are potentially life-threatening complications. [5]
Therapy and research directions.
NSAIDs may provide short-term symptom control in selected milder presentations, while glucocorticoids remain important for severe inflammation. Conventional disease-modifying antirheumatic drugs such as methotrexate or leflunomide may be used in selected settings, particularly for articular disease. IL-1 inhibitors, including anakinra and canakinumab, and IL-6 inhibition with tocilizumab are important biological approaches. They should not be presented solely as treatment after steroid failure: the 2024 EULAR/PReS recommendations prioritize early IL-1 or IL-6 inhibition, with glucocorticoid exposure kept as brief as feasible. [5,12]
Development is exploring the IL-1 family, IL-18, JAK signaling, interferon pathways, inflammasome regulation, and neutrophil activation, with programs at different preclinical and clinical stages. Interferon-γ blockade already has a specific regulatory role: in June 2025, the United States approved emapalumab for adults and children with hemophagocytic lymphohistiocytosis (HLH)/MAS in known or suspected Still’s disease who have an inadequate response or intolerance to glucocorticoids, or recurrent MAS. This is a complication-specific indication, not an approval for all AOSD presentations. [13]
The goals are rapid inflammatory control, lower glucocorticoid exposure, fewer relapses and severe complications, and more precise and safer individualized treatment.
Figure 5. AOSD pathophysiology and potential intervention points. Supplied figure from Bindoli et al. [5], Figure 1, © The Author(s) 2024; source license CC BY-NC 4.0. Created with BioRender.com. This 2024 map includes established, investigational, and preclinical approaches; inclusion does not establish efficacy or approval in AOSD.
[1] Gallo C, Dispinzieri G, Zucchini N, Invernizzi P, Massironi S. Autoimmune pancreatitis: Cornerstones and future perspectives. World J Gastroenterol. 2024;30(8):817–832. Source
[2] Wang H, Xie C, Deng B, et al. Structural basis for antibody-mediated NMDA receptor clustering and endocytosis in autoimmune encephalitis. Nat Struct Mol Biol. 2024;31(12):1987–1996. Source
[3] Cacoub P, Vieira M, Saadoun D. Cryoglobulinemia—One Name for Two Diseases. N Engl J Med. 2024;391(15):1426–1439. Source
[4] Hoffman RW, Maldonado ME. Immune pathogenesis of Mixed Connective Tissue Disease: a short analytical review. Clin Immunol. 2008;128(1):8–17. Source
[5] Bindoli S, Baggio C, Doria A, Sfriso P. Adult-Onset Still’s Disease (AOSD): Advances in Understanding Pathophysiology, Genetics and Emerging Treatment Options. Drugs. 2024;84(3):257–274. Source
[6] FDA. UPLIZNA (inebilizumab-cdon) prescribing information. IgG4-related disease indication added April 2025. Source
[7] Dubey D, Pittock SJ, Kelly CR, et al. Autoimmune encephalitis epidemiology and a comparison to infectious encephalitis. Ann Neurol. 2018;83(1):166–177. Source
[8] Abboud H, Probasco JC, Irani S, et al. Autoimmune encephalitis: proposed best practice recommendations for diagnosis and acute management. J Neurol Neurosurg Psychiatry. 2021;92:757–768. Source
[9] Wong KH, Day GS, Torner JC, et al. A Phase-2B Double-Blind Randomized International Prospective Trial of Inebilizumab in NMDAR Encephalitis: The ExTINGUISH Trial. Neurol Open Access. 2025;1(2):e000007. Source
[10] Quartuccio L, Bortoluzzi A, Scirè CA, et al. Management of mixed cryoglobulinemia with rituximab: evidence and consensus-based recommendations from the Italian Study Group of Cryoglobulinemia (GISC). Clin Rheumatol. 2023. Source
[11] Gunnarsson R, Molberg Ø, Gilboe IM, Gran JT. The prevalence and incidence of mixed connective tissue disease: a national multicentre survey of Norwegian patients. Ann Rheum Dis. 2011;70(6):1047–1051. Source
[12] Fautrel B, Mitrovic S, De Matteis A, et al. EULAR/PReS recommendations for the diagnosis and management of Still’s disease, comprising systemic juvenile idiopathic arthritis and adult-onset Still’s disease. Ann Rheum Dis. 2024. Source
[13] FDA. GAMIFANT (emapalumab-lzsg). Approval for HLH/MAS in known or suspected Still’s disease, June 27, 2025. Orphan Drug Designations and Approvals database. Source
Author: Bu Chi | Scientific review: Ding Ying | Editor: Jing Yan
HKeyBio, the autoimmune disease model specialist, is a preclinical contract research organization (CRO) focused on in vivo efficacy services for autoimmune disease. Its core technical team has more than 20 years of experience in autoimmune drug development. The company is ISO 9001 certified and operates molecular, cellular, pathology, small-animal, and analytical testing facilities in Suzhou Industrial Park, together with nonhuman primate research sites in Guangxi and Suzhou. The original company profile reports nearly 60 employees, with project leaders holding master’s or doctoral degrees, and team experience supporting more than 500 investigational new drug (IND) applications. The team specializes in addressing complex challenges during autoimmune drug development and regulatory submission.
· 50+ nonhuman primate models of autoimmune disease
· 300+ animal models of autoimmune disease
· Experience supporting 500+ IND applications in autoimmune diseases
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