Tryptase Immunoassays

Larry Schwartz:

http://www.aebm.org/jornadas/alergia/7.-%20Immunol%20Allergy%20Clin%20NA%202006.pdf

Mature(B)

Total (pro+mature (a+b))

Normal serum (ng/ml): Mature: <1 Total: 1-15

Systemic Anaphylaxis (acute): 

Mature: >1       Total: elev because mature is elevated

RATIO: Total/Mature <10

Syst Mastocytosis:

Mature: +/- Total: >20ng/ml

            RATIO:  Total/Mature  >20 because

                               protryptase (not mature) is elevated

>20

a/b-protryptases are spontaneously secreted by resting mast cells, 

In Mastocytosis the total tryptase is elevated related to total mast cell burden, but little mature tryptase is present.

Protryptases are represented in the numerator of the Total (a+b)/Mature(b) Tryptase Ratio, therefore the ratio is ELEVATED in mastocytosis

Total (a+b)/Mature(b) Tryptase Ratio 

in

Systemic Anaphylaxis

<10

mature b-tryptase is retained by mast cells until these cells are activated to degranulate.

Mature is in the denominator.

An increase in mature,  therefore make the ratio a very low number

Systemic Mastocytosis Diagnostic Criteria

Major

(1 major and 1 minor or >3 minor=dx)

1. Abnormal MC morphology ie spindle shaped
2. KIT mutation at codon 816
3. CD2 or CD25+ MC
4. Serum total tryptase >20

Differential DX of Elevated SerumTryptase

1. Systemic Mastocytosis
2. Hypereosinophilic syndrome FIP1L1-PDGFRA
3. AML (~30%)
4. Refractory anemias
5. Myleodysplasic syndromes
6. SCF administration
7. ESRD with elevated SCF
8. ?Transient mastocytosis
9. ?Normal variant

Increased suspicion for 

Mastocytosis

• Severe insect sting/venom reactions
• Idiopathic anaphylaxis
• Elevated baseline typtase
• Associated findings:  migraines (vascular headaches), gastritis or acid/peptic dz, unexplained flushing, bone pain (osteoclastic lesions on bone scan)

Cellular defect associated with

Systemic Mastocytosis

c-Kit mutations 

ie D816V

 ie  there is a mutation in  c-Kit or Mast/stem cell growth factor receptor (SCFR)  (CD117)

Immunophenotype of Bone Marrow MC  

in System Mastocytosis

Mutation in

Systemic Mastocytosis with Eosinophilia 

KIT D816V

(c-Kit mutation)

(Differentiated from CEL chronic eosinohillic leukemia with mutation FIP1L1/PDGFR)

Staging systemic mastocytosis

I.   Cutaneous (UP, DCM, MP, mastocytoma)

II.  Indolent (isolated BM, smoldering)          40% w/ c-Kit mutations

III. Systemic w assoc clonal hematologic disorder (AML MDS MPD, CMML, NHL, CEL)  40% w/ c-Kit mutations

IV. Systemic aggressive (+LAN and eosinophiia)  12% w/ c-Kit mutations

V.  Mast cell leukemia    1% w/ c-Kit mutations

VI. Extracutaneous mastocytoma

Severe Anaphylaxis with 

Insect sting/venom

• correlates with baseline total trytase
• may be evidence for mast cell clonality (mastocytosis)

PAF and anaphylaxis severity

Low PAF acetyl hydrolase levels/ 

high PAF:

increased severity in food induced anaphylaxis

Anaphylaxis  

without 

tryptase elevations

• Food induced anaphylaxis: tryptase often not elevated
• Local mast cel-mediated angioedema (laryngeal)
• Mast cells far from circulation (mucosal vs perivascular) 
• Mast cells w less tryptase (MCt<MCtc)
• Non-mast cell mediated (basophils)
• Late phase (baso/eos) vs early (mast cell)

Evidence of constituitive

Mast Cell activation

in human asthma

• Elevated histamine and tryptase in BALF
• Elevated PGD2 in BALF
• Increased MC # in airway smooth muscle in asthmatics