Table I.

Classical Complement Pathway Triggering of Promastigote-C3 Opsonization by Natural Anti-Leishmania Antibodies

Incubation		Promastigote bound C3 (%)
30 s	120 s	L. amazonensis (n)	L. donovani (n)
PBS	NHS	100	100
PBS	NHS-EGTA	8.3 ± 1.7 (4)	3.2 ± 0.4 (4)
PBS	IgM	2.8 ± 1.2 (6)	3.0 ± 1.4 (6)
PBS	IgG	0.8 ± 0.6 (3)	0.6 ± 0.6 (4)
PBS	Ads-NHS	15.1 ± 2.0 (15)	11.4 ± 1.1 (24)
NHS-EDTA	NHS	100	100
NHS-EDTA	Ads-NHS	88.8 ± 4.8 (15)	71.7 ± 5.3 (26)
IgM-EDTA	Ads-NHS	88.6 ± 2.7 (13)	93.8 ± 3.6 (13)
IgG-EDTA	Ads-NHS	17.8 ± 1.4 (13)	17.4 ± 2.9 (13)

Promastigote triggering of complement activation was analyzed in a two-step binding assay. Promastigotes were preincubated (37°C, 30 s) in 100 μl of PBS, NHS-EDTA, IgM-EDTA, or IgG-EDTA as indicated, washed twice by centrifugation, and incubated (37°C, 120 s) in the conditions indicated. Samples then were processed as described (Materials and Methods). Results are expressed as the percentage of maximum promastigote-bound C3 in NHS (100%) = SEM; (n), number of experiments performed.