ASCA and ANCA: the pathway in the body

This page shows the biochemical pathway behind the laboratory value ASCA, ANCA: which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

ASCA and ANCA are antibodies in the blood: ASCA are directed against mannan from the yeast cell wall, ANCA against proteins of neutrophil granulocytes. They form when immune cells classify these structures as foreign, and then bind specifically to their target.

The pathway step by step

Each station states what the compound does there. Three signs: ↑ supplies — builds up or makes available · ↓ depletes — inhibits, consumes or withholds · ↕ both, depending on amount. Behind it stands what the statement rests on: established physiology, observed in studies, or contested. The signs do not grade; they name the direction.

1. Yeast in the gut → Mannan Mannan is a chain of the sugar mannose on the outside of the yeast cell wall. ASCA recognise short stretches of several mannose units within it (oligomannose). Source 1↑ supplies Mannan is the part of the yeast that the immune system meets first. Particular linkages of the mannose units form the site to which ASCA bind. observed in studies Source 1
   ⚖ When the balance tips

   too much — If plenty of mannan is present at the gut lining, more immune cells meet it, and the stimulus for antibody formation becomes stronger.

   too little — If little mannan is present or the matching linkages are missing, as in other yeast species, ASCA bind weakly or not at all.

   observed in studies · Source 1, 2

2. Mannan → Across the gut lining Special cells over the lymphoid follicles of the gut, the M cells, ferry particles from the gut contents inwards. There dendritic cells pick them up and present them to B and T cells. Source 3↑ supplies This route is the gut’s normal sampling system: it lets the immune system inspect components of the gut contents before they penetrate deeper. established physiology Source 3
   ⚖ When the balance tips

   too much — If the gut lining is irritated or more permeable, more yeast components get inside, and immune cells meet mannan more often.

   too little — If little gets inside, immune cells rarely contact yeast mannan, and hardly any antibodies are formed against it.

   observed in studies · Source 3, 2

3. Across the gut lining → Plasma cell · Retinoic acid When a B cell recognises mannan and receives help from T cells, it divides and matures into a plasma cell. This releases large amounts of a single antibody. Source 4↑ supplies Plasma cells are antibody factories. In the gut lining mainly IgA-producing cells arise; IgG and IgA reach the blood, where they can be measured. established physiology Source 4, 10
   ⚖ When the balance tips

   too much — If the immune system meets mannan repeatedly, more and longer-lived plasma cells form, and the amount of ASCA in the blood rises.

   too little — If hardly any plasma cells against mannan are formed, ASCA in the blood stay low.

   established physiology · Source 4

4. Plasma cell → ASCA ASCA (anti-Saccharomyces cerevisiae antibodies) are IgG and IgA antibodies against yeast mannan. They circulate in the blood and are measured in serum. Source 1↓ depletes ASCA bind mannan on yeast cells and thus mark them for phagocytes. Because Candida carries similar mannan stretches, they recognise this yeast too. observed in studies Source 1, 2
   ⚖ When the balance tips

   too much — If there are many ASCA in the blood, yeast components that pass the gut lining are bound and cleared more quickly.

   too little — If there are few ASCA in the blood, other parts of the defence clear yeast components; a low level on its own says little about the gut lining.

   observed in studies · Source 1

   Field of research — ASCA are being studied as antibody markers in inflammatory bowel conditions. Source 5

5. ASCA → Binding to mannan The antibody’s binding site fits a particular sequence of mannose units. The same sequence occurs in Saccharomyces and in Candida albicans. Source 1, 2↓ depletes Bound mannan is marked for phagocytes. Because Candida carries the same sequence, studies regard it as one trigger of ASCA formation. observed in studies Source 2
   ⚖ When the balance tips

   too much — If many antibodies bind yeast mannan, Candida cells are marked too; in animal models ASCA rose when Candida colonised the gut.

   too little — If few antibodies bind, yeast mannan stays largely unmarked and is cleared by other routes.

   observed in studies · Source 2

6. Neutrophils → Target structures Classic ANCA are directed against PR3 or MPO from the granules. Atypical ANCA instead recognise proteins at the edge of the nucleus, such as one form of beta-tubulin. Source 6, 7, 8↑ supplies The structure an antibody recognises determines its staining pattern under the microscope: PR3 stains the cytoplasm, MPO the rim of the nucleus, atypical ANCA the nuclear envelope. observed in studies Source 6, 7
   ⚖ When the balance tips

   too much — If these proteins are exposed, for example when neutrophils break apart or cast out DNA nets, the immune system comes into contact with them more often.

   too little — If the proteins stay hidden inside the cell, the immune system barely sees them, and tolerance towards them is maintained.

   observed in studies · Source 6

7. Target structures → ANCA formed ANCA are autoantibodies: the immune system makes them against the neutrophils’ own proteins. How tolerance is broken in the process is only partly understood. Source 6↕ both, depending on amount The antibodies formed target the body’s own defence cell. Depending on the target they have no recognisable effect or activate neutrophils; infections and medicines are discussed as triggers. contested Source 6
   ⚖ When the balance tips

   too much — If many ANCA are formed, more antibodies bind their target; with PR3 and MPO, studies show more neutrophils being activated as a result.

   too little — If hardly any ANCA are formed, tolerance towards the neutrophils’ proteins is maintained, and the serum test is negative.

   observed in studies · Source 6

8. ANCA formed → Atypical ANCA Under the microscope, atypical ANCA stain the nuclear envelope. They are therefore also called antineutrophil nuclear antibodies and are measured in serum. Source 7↕ both, depending on amount Atypical ANCA bind to proteins of the nuclear envelope. Whether they have an effect of their own is unclear; they are regarded more as companions of an immune response than as its cause. contested Source 7, 8
   ⚖ When the balance tips

   too much — Many atypical ANCA in the blood indicate a lasting response against proteins of the nuclear envelope; a link to gut bacteria is being studied.

   too little — If no atypical ANCA are detectable, this antibody response is absent; on its own this says little about the gut lining.

   contested · Source 7, 8

   Field of research — Atypical ANCA are being studied in inflammatory conditions of the bowel and bile ducts. Source 5

9. ANCA formed → PR3 and MPO ANCA Classic ANCA bind to proteinase 3 or myeloperoxidase. MPO contains an iron-containing haem and produces hypochlorite against microbes inside neutrophils. Source 6, 9↕ both, depending on amount When these ANCA bind PR3 or MPO on the cell surface, the neutrophils are activated. Defence tools then also act where there are no microbes. observed in studies Source 6
   ⚖ When the balance tips

   too much — If many of these ANCA are present, more neutrophils are activated prematurely and release enzymes and oxygen radicals at the vessel wall; shown in animal models.

   too little — Without these antibodies, PR3 and MPO remain purely defence tools inside the granules.

   observed in studies · Source 6

10. Atypical ANCA → Cross-reaction Atypical ANCA against beta-tubulin also recognise FtsZ, a similarly built protein of many bacteria. This suggests that bacteria can set off their formation. Source 8↕ both, depending on amount An antibody first formed against a bacterial protein can spill over to a similar body protein. Whether this is how atypical ANCA arise is not established. contested Source 8
    ⚖ When the balance tips

    too much — If the immune system often meets FtsZ from gut bacteria, it may form more cross-reacting antibodies; so far this is shown only in laboratory experiments.

    too little — If contact with FtsZ is low, this possible trigger is absent.

    contested · Source 8

11. PR3 and MPO ANCA → Neutrophils activated When PR3 or MPO ANCA bind to primed neutrophils, these release oxygen radicals and enzymes and cast out DNA nets. Source 6↓ depletes The released substances act not only against microbes but also against the cells of the vessel wall to which the neutrophils adhere. observed in studies Source 6
    ⚖ When the balance tips

    too much — If many neutrophils are activated this way, the tissue around small vessels is attacked more strongly; in animal models the complement system amplifies the process.

    too little — If hardly any neutrophils are activated, the antibodies have no such effect at the vessel wall.

    observed in studies · Source 6

Further stations

• Yeast in the gut — Saccharomyces cerevisiae Baker’s yeast, Saccharomyces cerevisiae, reaches the gut with bread, beer and other foods. Related yeasts such as Candida albicans also live there permanently. Source 1, 2↑ supplies Yeasts bring cell-wall components into the gut that the immune system can recognise as foreign. Mostly they stay in the gut contents and hardly come into contact with immune cells. observed in studies Source 2
  ⚖ When the balance tips

  too much — If many yeasts reach the gut or Candida multiplies there, more yeast mannan is available as a stimulus; in animal models colonisation with Candida led to ASCA formation.

  too little — If few yeasts reach the gut, the immune system rarely meets yeast mannan, and there is little occasion to form antibodies against it.

  observed in studies · Source 2

• Neutrophils — white blood cells Neutrophil granulocytes are the most common white blood cells. In their granules and at the nucleus they carry proteins that ANCA can target. Source 6, 7↑ supplies Neutrophils break down engulfed microbes with enzymes such as proteinase 3 (PR3) and myeloperoxidase (MPO). These enzymes are also the best-known targets of ANCA. established physiology Source 6, 9
  ⚖ When the balance tips

  too much — If many neutrophils are primed by signalling molecules, they carry more PR3 and MPO on their surface, where antibodies can reach them.

  too little — If neutrophils are at rest, PR3 and MPO stay largely inside the granules and are hard for antibodies to reach.

  observed in studies · Source 6

Cofactors in this pathway

• Mannose — Sugar unit of yeast mannan; particular mannose chains form the binding site of ASCA Source 1
• Iron — Sits in the haem of myeloperoxidase, a target enzyme of ANCA, and is needed for its hypochlorite production Source 9In the ORY catalogue as a laboratory value: Eisen
• Vitamin A (retinoic acid) — Needed as retinoic acid for B cells in the gut to become IgA-producing, gut-homing cells Source 10
• Vitamin D — Slows the maturation of B cells into plasma cells and their antibody production in cell culture Source 11In the ORY catalogue as a laboratory value: Vitamin D

Sources

1. Sendid B, Colombel JF, Jacquinot PM et al. Specific antibody response to oligomannosidic epitopes in Crohn's disease. Clin Diagn Lab Immunol 1996 · PubMed 8991640
2. Standaert-Vitse A, Jouault T, Vandewalle P et al. Candida albicans is an immunogen for anti-Saccharomyces cerevisiae antibody markers of Crohn's disease. Gastroenterology 2006 · PubMed 16697740
3. Mabbott NA, Donaldson DS, Ohno H et al. Microfold (M) cells: important immunosurveillance posts in the intestinal epithelium. Mucosal Immunol 2013 · PubMed 23695511
4. Nutt SL, Hodgkin PD, Tarlinton DM et al. The generation of antibody-secreting plasma cells. Nat Rev Immunol 2015 · PubMed 25698678
5. Mitsuyama K, Niwa M, Takedatsu H et al. Antibody markers in the diagnosis of inflammatory bowel disease. World J Gastroenterol 2016 · PubMed 26811667
6. Jennette JC, Falk RJ. Pathogenesis of antineutrophil cytoplasmic autoantibody-mediated disease. Nat Rev Rheumatol 2014 · PubMed 25003769
7. Terjung B, Worman HJ, Herzog V et al. Differentiation of antineutrophil nuclear antibodies in inflammatory bowel and autoimmune liver diseases from antineutrophil cytoplasmic antibodies (p-ANCA) using immunofluorescence microscopy. Clin Exp Immunol 2001 · PubMed 11678897
8. Terjung B, Söhne J, Lechtenberg B et al. p-ANCAs in autoimmune liver disorders recognise human beta-tubulin isotype 5 and cross-react with microbial protein FtsZ. Gut 2010 · PubMed 19951907
9. Klebanoff SJ. Myeloperoxidase: friend and foe. J Leukoc Biol 2005 · PubMed 15689384
10. Mora JR, Iwata M, Eksteen B et al. Generation of gut-homing IgA-secreting B cells by intestinal dendritic cells. Science 2006 · PubMed 17110582
11. Chen S, Sims GP, Chen XX et al. Modulatory effects of 1,25-dihydroxyvitamin D3 on human B cell differentiation. J Immunol 2007 · PubMed 17641030

Related pathways

• ACE2 and GM-CSF autoantibodies — plasma cell
• Borrelia — target structures
• Clostridioides difficile — neutrophils
• Calprotectin — neutrophils
• Candida — neutrophils

As of 2026-10-05. Draft, written by Claude to schema v2; sources checked in PubMed; expert approval pending
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