"HTLA" is an umbrella term for antibodies that have similar characteristics despite not being associated with the same blood group systems. Understanding these characteristics is key to conducting antibody identification studies. The acronym "HTLA" encapsulates the two primary features of these antibodies:
- High Titer: The titration procedure is a method to roughly quantify the concentration of antibody. "HTLA" antibodies typically show reactivity at dilutions of 1:32 or 1:64 when serially diluted. However, it's not uncommon for them to maintain reactivity at even lower concentrations.
- Low Avidity: This refers to the weak binding force between the immunoglobulin G (IgG) molecule and its target epitope. The strength of reaction 0–4+ is used to distinguish avidity. This characteristic is observable during macroscopic examination of agglutination in a test tube; reactions are weak at the Anti-Human Globulin (AHG) phase and are more prone to break apart compared to typical red cell antigen-antibody complexes meaning a low strength of binding between IgG and its target epitope.
The table shows some examples of different reactivity patterns when performing an antibody titration.
| Titer Examples | 1:1 | 1:2 | 1:4 | 1:8 | 1:16 | 1:32 | 1:64 | 1:128 | 1:256 | 1:512 | 1:1024 | 1:2048 |
Low Titer
Low Avidity | W+ | W+ | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Low Titer
High Avidity | 3+ | 2+ | 2+ | 1+ | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
High Titer
Low Avidity | 1+ | 1+ | 1+ | 1+ | W+ | W+ | W+ | W+ | 0 | 0 | 0 | 0 |
High Titer
High Avidity | 3+ | 3+ | 3+ | 3+ | 2+ | 2+ | 2+ | 2+ | 1+ | 1+ | 1+ | 1+ |
