Pathogenesis of scleroderma: cells and mediators
The development of scleroderma begins with primary vascular injury, which entails tissue ischemia, endothelial dysfunction, and local thrombosis. In response, a cascade of immunological reactions aimed at fibrosis formation is triggered. Several key cell populations are involved in this process:
- Activated platelets. They release platelet-derived growth factor — PDGF (Platelet-derived growth factor). This mediator directly stimulates the differentiation and subsequent proliferation of fibroblasts.
- Th2 lymphocytes (Type 2 T-helper cells). These cells actively secrete interleukins IL-4 and IL-13, sustaining the inflammatory and fibrogenic response.
- Activated macrophages. They act as the primary source of TGFβ (transforming growth factor beta), which is critical for enhancing collagen synthesis.
The natural outcome of such coordinated cellular activity is massive sclerosis of the connective tissue and irreversible obliteration (closure of the lumen) of blood vessels.
Role of autoantibodies and cytokine balance
Scleroderma is characterized by the detection of antinuclear antibodies, as well as specific immunoglobulins against connective tissue proteins — topoisomerase and fibrillin-1.
Of particular importance are anti-fibrillin-1 antibodies. Their binding leads to direct activation of fibroblasts. Activated fibroblasts upregulate the expression of various extracellular matrix components, including metalloproteinases. This promotes the release of TGFβ from tissue depots, closing the vicious circle and dramatically accelerating the development of fibrosis.
The disease is based on a shift in the cytokine profile:
- Profibrogenic factors (predominant): TGFβ, Th2 cell cytokines, and the chemokine MCP-1 (responsible for recruiting new fibroblasts to the lesion site).
- Antifibrogenic factors (suppressed): Th1-profile cytokines such as IFNγ and TNFα (which inhibit fibrosis).
It is important to note that Th2 cytokines not only stimulate fibrosis but also promote autoantibody production by autoreactive B lymphocytes.
Related autoimmune conditions: Sjögren's syndrome
Sjögren's syndrome is another chronic autoimmune disease, but with different target organs. The exocrine glands are primarily affected: lacrimal, salivary, and parotid glands. In later stages, the muscular tissue, blood vessels, kidneys, and nervous system become involved.
The key pathogenetic link is massive infiltration of the exocrine glands by activated T and B lymphocytes. Autoreactive CD4+ T cells play the main role in the destruction and dysfunction of the glands. Concurrently, polyclonal B-cell activation occurs, with the cytokine BAFF acting as a crucial stimulus. The produced autoantibodies are used in clinical diagnostics, although their direct pathogenetic role has not yet been established.
Systemic lupus erythematosus (SLE)
SLE is a severe systemic autoimmune disease associated with high mortality. The etiology is not fully understood, but viral infection is hypothesized to be the trigger. Cofactors play an important role: ultraviolet radiation and hormonal imbalance. The predominance of estrogens has been proven — over 90% of SLE patients are women.
The pathogenesis is based on multiple immunological disorders dominated by autoimmune inflammation (a single leading factor cannot be singled out).
Tissue damage mechanism:
- The main manifestation of the disease is the synthesis of autoantibodies against a vast number (over 100) of self-antigens. Antibodies to double-stranded DNA predominate (found in 95% of patients).
- Antibodies bind to autoantigens, forming immune complexes.
- SLE is characterized by complement system deficiency. Due to a shortage of the C3b component, the clearance (removal) of these complexes from the bloodstream is slowed down, leading to their deposition in tissues and severe organ damage.
Briefly: answers to topical questions
What specific autoantibodies are characteristic of systemic sclerosis?
Systemic sclerosis is characterized by the detection of antinuclear antibodies and antibodies to connective tissue proteins. Serological markers include:
- Anti-topoisomerase I antibodies (Scl-70).
- Anticentromere antibodies.
- Anti-fibrillin-1 antibodies — activate fibroblasts and promote the development of fibrosis.
- Anti-fibrillarin antibodies and PM-Scl.
- Anti-RNA polymerase I or III antibodies.
What clinical forms of systemic sclerosis are distinguished in the classification?
The classification of systemic sclerosis distinguishes two main and several special clinical forms.
- Diffuse scleroderma (dSSc) — characterized by widespread skin involvement and early internal organ involvement.
- Limited scleroderma (lSSc) — manifests as specific involvement of the skin of the face, forearms, and fingers, with visceral changes developing later.
Special forms include:
- Overlap syndrome (overlap) is a combination with features of other diseases (rheumatoid arthritis, dermatomyositis, systemic lupus erythematosus).
- CREST syndrome — includes calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, and telangiectasia.
Which specific autoantibodies are diagnostic markers for Sjögren's syndrome?
Diagnostic markers for primary and secondary Sjögren's syndrome are antinuclear factor and specific autoantibodies. The classification criteria for the disease include:
- Antinuclear factor (ANF Hep2).
- Anti-Ro antibodies (Ro/SS-A) — antibodies to RNA and RNA polymerase.
- Anti-La antibodies (La/SS-B) — antibodies to a protein complexed with RNA.
The pathogenetic role of these autoantibodies has not been established, but their detection in blood serum is necessary to confirm the diagnosis.
Which specific autoantibodies are detected in systemic lupus erythematosus?
Systemic lupus erythematosus is characterized by the detection of numerous autoantibodies, among which highly specific markers and antiphospholipid antibodies stand out. The main diagnostic markers include:
- Anti-double-stranded DNA antibodies (anti-dsDNA) — dominant antibodies detected in 95% of patients.
- Anti-Smith antibodies (anti-Sm) — highly specific antinuclear antibodies.
- Antinuclear factor (ANF) on HEp-2 cells and an antinuclear antibody panel.
- Antiphospholipid antibodies — include anticardiolipin antibodies, anti-β2-glycoprotein I antibodies (anti-β2-GPI), and lupus anticoagulant.
To remember the profibrogenic profile of scleroderma, use the "Rule of 3 Macro-T's": Platelets (release PDGF), T-helper 2 (IL-4, IL-13), and Transforming growth factor (TGFβ from macrophages) — all lead to Tissue sclerosis.
Class and exam questions
What event triggers the development of scleroderma?
The process is triggered by vascular injury. This leads to ischemia, endothelial dysfunction, and local thrombosis, which activates immune cells.
How do antibodies against fibrillin-1 enhance fibrosis?
They activate fibroblasts, prompting them to synthesize metalloproteinases and other matrix components. This releases the profibrogenic factor TGFβ from tissue depots.
What are the main target organs in Sjogren's syndrome?
The primary targets are exocrine glands: salivary, lacrimal, and parotid. Glandular dysfunction is driven by infiltration with autoreactive CD4+ T cells.
Why do immune complexes damage organs in SLE instead of being cleared from the body?
Patients with SLE frequently exhibit complement deficiency. The complexes contain little of the C3b component, causing their clearance by phagocytes to be critically slowed down.
What else to study on this topic
- Mechanisms of endothelial injury and ischemia development in autoimmune pathologies
- Properties and functions of transforming growth factor beta (TGFβ)
- The role of the BAFF cytokine in B-lymphocyte activation
- Complement system: mechanisms of immune complex elimination via C3b
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