FIGURE 9.

Cleaved A2M retains its ability to enhance SP-D-mediated E. coli agglutination. A, SP-D, but not cleaved A2M, is able to agglutinate bacteria and cause a reduction in the A_{600 nm}. Cleaved A2M (50 or 5 μg/ml) or SP-D (1 μg/ml) was added to 200 μl of E. coli suspension in the presence of 5 mm CaCl₂. The addition of cleaved A2M premixed with SP-D greatly enhances the agglutination of bacteria. Cleaved A2M (50 or 5 μg/ml) and SP-D (1 μg/ml) were pre-mixed for 1 h at 37 °C in the presence of 5 mm CaCl₂ prior to being added to 200 μl of bacterial suspension. ●, bacteria alone; ■, bacteria + 1 μg/ml SP-D; ▴, bacteria + 50 μg/ml cleaved A2M; ▾, bacteria + 5 μg/ml cleaved A2M; ♦, bacteria + 50 μg/ml cleaved A2M and 1 μg/ml SP-D premixed; ×, bacteria + 5 μg/ml cleaved A2M and 1 μg/ml SP-D premixed. All values are significantly different from the SP-D alone condition (p < 0.01). B, pre-mixing the bacteria with cleaved A2M enhanced E. coli agglutination by SP-D, but not as much as pre-mixing the SP-D and cleaved A2M prior to addition to the bacterial suspension. Cleaved A2M (50 or 5 μg/ml) was mixed with the bacteria suspension for 1 h at 37 °C prior to SP-D (1 μg/ml) addition in the presence of 5 mm CaCl₂. ●, bacteria alone; ■, bacteria + 1 μg/ml SP-D; ▴, bacteria pre-mixed with 50 μg/ml cleaved A2M then 1 μg/ml SP-D; ▾, bacteria pre-mixed with 5 μg/ml cleaved A2M then 1 μg/ml SP-D. E. coli experiments were conducted at the same time but plotted separately for clarity (A and B). All values are significantly different from the SP-D alone condition (p < 0.01).