Figure 8. T2Q cells can be protected by Qdm peptide either by preloading or by the inclusion of peptide in the cytotoxicity assay

Preloaded

Inclusion

AIMV

26^o

AIMV

37^o

D10F

26^o

D10F

37^o

Lytic units/thousand effectors

The data in the left hand panel shows the results of preloading T2Q cells by incubating them

overnight at 26^o or 37^o with 100uM Qdm peptide in serum free AIMV or serum-containing

D10F medium, then washing them free of exogenous peptide prior to cytotoxicity assay.

The data in the right hand panel shows the result of adding 100uM Qdm peptide just before

setting up cytotoxicity assays [ie. peptide present in the assay] to T2Q cells that had been

incubated overnight in serum-free or serum-containing medium at 26^o or 37^o.

In both cases, T2Q cells were mixed with graded doses of Qa1R⁺ NK cells and susceptibility

to lysis calculated by regression analysis of the linear part of the dose-response.

Conclusions

1. Protection of T2Q cells from NK lysis can be achieved as effectively by preloading them at 37^o

as by preloading them at 26^o, provided serum-free medium is used

2. In the presence of serum, protection cannot be achieved at 37^o due to the inactivation of Qdm

peptide, presumably by peptidases present in serum

3. Surprisingly, T2Q cells could be protected by adding peptide to them just before mixing them

with effectors, demonstrating that protective Qa1-Qdm complexes form very quickly, presumably

at the cell surface. [See Figure 10 for confirmation of the rapid kinetics of protection.]

4. T2Q cells that had been preincubated at 26^o or 37^o in the presence or absence of serum

could be equally effectively protected in this manner