. 2013 Jun;81(6):1880–1888. doi: 10.1128/IAI.01328-12

Table 2.

FIC indices for multiple MAb interactions

MAb(s)^a	Survival (%)			Ab concn (μg/ml) for 50% survival	FIC^b	FIC index^c
MAb(s)^a	Maximum	Minimum	50%	Ab concn (μg/ml) for 50% survival	FIC^b	FIC index^c
Δ17F1	58.76	28.74	43.75	0.05
Δ20C1	124.55	33.88	79.22	0.18
Δ17F1 + 20C1	139.05	114.26	126.65	0.01	0.28
Δ20C1 + 17F1	137.07	59.79	98.43	0.11	0.61	0.89
Δ17F1	60.35	28.96	44.65	0.40
Δ19C9	40.28	34.10	37.19	0.05
Δ17F1 + 19C9	55.28	31.18	43.23	0.18	0.45
Δ19C9 + 17F1	60.21	40.63	50.42	1.25	25.50	25.96
Δ17E7	90.98	70.28	80.63	11.10
Δ19C9	84.71	66.93	75.82	39.80
Δ17E7 + 19C9	78.81	67.95	73.38	2.37	0.21
Δ19C9 + 17E7	85.44	72.83	79.14	0.04	1,130.68	1,130.90
Δ20C1	54.30	17.00	35.65	2.95
ΔN5C10	63.58	15.88	39.73	0.43
Δ20C1 + N5C10	83.99	60.04	72.01	0.04	0.02
ΔN5C10 + 20C1	90.58	39.48	65.03	0.08	0.20	0.21
Δ20C1	44.84	11.94	28.39	1.62
Δ19D9	73.42	12.31	42.86	1.79
Δ20C1 + 19D9	92.71	61.29	77.00	0.41	0.26
Δ19D9 + 20C1	96.48	22.79	59.63	0.27	0.15	0.41

MAbs preceded by a Greek capital delta (Δ) are “variable antibodies,” i.e., used at various concentrations (see Fig. 4 and 5).

FIC was calculated as follows: Ab concentration of the variable antibody A that yields 50% of maximum cell survival when in combination with a constant concentration of antibody B divided by the Ab concentration at 50% of maximum cell survival with antibody A alone.

The FIC index was defined as the sum of the FICs for each antibody pair. An interaction is defined as synergistic at an FIC index of <1, additive at an FIC index of 1, indifferent at an FIC index between 1 and 2, and antagonistic at an FIC index of >2. Adapted from references 27, 28, and 29.