15.2 Enzymes, Enhancement Media, and Lectins

15.2 Enzymes, Enhancement Media, and Lectins

Quick Answer: Ficin, papain, trypsin, and bromelin destroy Fya, Fyb, M, and N, destroy S variably, and enhance Rh, Kidd, Lewis, I, and P1. Two-stage enzyme treatment (pretreat cells, wash, then add serum) is cleaner and more sensitive than one-stage. LISS lowers zeta potential and shortens incubation. PEG concentrates antibody and may enhance warm autoantibodies — some laboratories skip PEG when an auto is present. Albumin is the historical potentiator. Lectins: Dolichos biflorus = A1, Ulex europaeus = H, Vicia graminea = N, Arachis hypogaea = T, Glycine max = T/Tn, Salvia = Tn.

The June 9, 2026 outline lists enzymes, enhancement media, and lectins under IV.C. Chapters 6–9 already used the enzyme row as a system fingerprint. This section is the technique: which protease, which stage, which potentiator, and which plant protein is pretending to be an antibody.

Four proteases, one teaching table

Ficin (fig), papain (papaya), trypsin (pancreas), and bromelin (pineapple) are proteolytic enzymes. They cleave sialic-acid-rich glycoproteins off the red-cell surface. Antigen loss is not random. Structures that live on the cleaved N-terminus disappear. Structures that sit deeper, or that become easier to reach after the glycocalyx is shaved, get stronger.

Memorize the destroy list the outline named: Fya, Fyb, M, N, S (variable). Memorize the enhance list: Rh, Kidd, Lewis, I, P1. Kell staying put is the contrast that keeps you out of the DTT chapter until you belong there.

Enzymes also destroy or weaken Ch/Rg, Xga, JMH, and some Ge/Yt antigens. That is useful in a high-prevalence workup, not a reason to forget Duffy.

One-stage versus two-stage

One-stage: enzyme, serum, and cells go into the same tube and incubate together. It is fast. It is less sensitive, and leftover protease plus serum can produce nonspecific agglutination. Use it as a screen-style shortcut, not as your only identification method.

Two-stage: pretreat the reagent cells with enzyme, wash the enzyme away, then add serum (or plasma) and incubate. Washing removes unbound protease so it cannot chew the antibody. Two-stage is more sensitive and cleaner and is the method BB expects when the stem says “enzyme-treated panel.”

If an untreated panel looks like anti-Fya plus something else, the enzyme panel should drop the Duffy rows and leave the second specificity standing. If everything gets stronger, you are in Rh/Kidd/Lewis/I/P1 territory, not Duffy.

LISS lowers zeta and shortens incubation

Red cells in normal saline carry a negative surface charge. The zeta potential is the energy barrier that keeps them apart. IgG is too small to bridge that gap by itself, which is why you need AHG or a potentiator.

Low-ionic-strength saline (LISS) reduces the Na+ cloud around the cell. Antibody association speeds up, so 37 °C incubation drops from the old 30–60 minutes in saline/albumin to about 10–15 minutes. That is the operational reason every tube bench owns LISS.

LISS is not magic protein. Rules that fail people:

• Serum-to-cell-to-LISS ratio is sacred. Dumping extra serum into a LISS tube raises ionic strength and you lose the kinetic advantage — and you can miss an antibody.
• LISS can enhance cold autoantibodies. A panagglutinin that appeared only after LISS is not automatically anti-Jka.
• LISS does not destroy antigens. Do not use a LISS-negative, enzyme-positive pattern as if LISS were ficin.

PEG concentrates antibody — and warm autos

Polyethylene glycol (PEG) is a water-exclusion agent. It concentrates immunoglobulin at the cell surface and is the most sensitive common tube potentiator. Weak Kidd and Duffy antibodies that saline or LISS missed often appear in PEG-AHG.

The same physics is why PEG may enhance warm autoantibodies. A patient with a warm auto can become panreactive in PEG when a LISS or saline IAT was workable. Some laboratories skip PEG (or switch methods) when an autoantibody is present so they can still see an alloantibody. That sentence is an outline-level fact, not a local quirk.

Do not read a PEG tube at 37 °C. PEG creates sludge that looks like 4+ agglutination. Wash, add AHG, and read the AHG button. Incomplete washing after PEG is a favorite false-positive.

Albumin is historical

22% bovine albumin was the classic zeta-reducing potentiator. Incubation was long. Sensitivity is lower than LISS or PEG for most IgG antibodies. You will still see albumin in old procedures, some Rh slide methods, and as a protein control for high-protein reagents. You will not choose albumin over LISS or PEG to “increase sensitivity” on a current-method item.

Lectins: plant proteins with blood-group jobs

A lectin is a plant (or invertebrate) protein that binds a carbohydrate epitope. It is not an immunoglobulin. It is a reagent that mimics a specificity.

Dolichos at the A1 typing dilution is anti-A1. Do not call every Dolichos reaction Tn. Dilution and context decide. Ulex is how you prove Bombay (Oh) — no H on cells, and the serum behaves like anti-H. Vicia is the N lectin; it is not anti-M. Peanut and soybean are polyagglutination reagents, not ABO reagents.

Run a lectin panel on washed cells with the manufacturer’s dilution. Unwashed plasma protein and bacterial contamination invent extra reactions.

Exam traps

• Saying enzymes destroy Kell or Kidd. They enhance Kidd and leave Kell.
• Treating S as always destroyed. S is variable.
• Using a one-stage enzyme result as if it were a washed two-stage panel.
• Adding extra serum to a LISS tube and wondering why the screen went silent.
• Reading PEG at 37 °C or insisting on PEG in a raging warm auto.
• Mixing lectins: Dolichos is A1, Ulex is H, Vicia is N, peanut is T, Salvia is Tn.