Table 2.

Sensitivity of OPKA-1A, OPKA-2A, and OPKA-3 methods for the detection of antibody-dependent killing

Expt	OPKA variant	Target S. pneumoniae strain	Phagocytosis assay incubation conditions (°C, % CO2, time)a	OPKA titers
				Pool 22b	Anti-clade 2 PspAc	Anti-PR domainc	NRSd
A	OPKA-1Be	TRE118	BRC (37°C, 5% CO2, 30 min); HL-60 (37°C, 5% CO2, 45 min)	1,962	352	133	<4
A	OPKA-1Cf	TRE118	BRC + HL-60 (37°C, 5% CO2, 75 min)	2,621	1,054	249	<4
B	OPKA-1Ag	D39	BRC + HL-60 (37°C, 5% CO2, 45 min)	720	8	41	NTh
B	OPKA-1A	TRE118	BRC + HL-60 (37°C, 5% CO2, 45 min)	2,261	322	198	NT
B	OPKA-1C	D39	BRC + HL-60 (37°C, 5% CO2, 75 min)	836	106	64	NT
B	OPKA-1C	TRE118	BRC + HL-60 (37°C, 5% CO2, 75 min)	2,785	1,542	405	NT

^aIn experiments A and B, the critical differences in assay conditions are incubation times and whether the BRC is incubated alone with the bacteria prior to addition of HL-60 cells (OPKA-1B) or if BRC and HL-60 cells are both added to the bacteria prior to a single incubation period.

^bPool 22 (38) is a pool of normal human serum that contains antibodies to most capsular polysaccharides, including capsular type 2.

^cRabbit antisera to the α-helical regions of clade 2 (50) PspA and to a proline-rich (PR) domain of PspA, including the nonproline block (33).

^dNRS, nonimmune normal rabbit serum.

^eIn OPKA-2B, the opsonized target cells are incubated first with BRC for 30 min and then HL-60 cells are added and incubated for another 45 min.

^fOPKA-2C is a modification of the OPKA-2A, where the incubation time with complement and HL-60 cells was extended from 45 to 75 min.

^gStandard UAB OPKA, where the opsonized target cells are incubated with BRC and HL-60 cells for 45 min.

^hNT, not tested.