TABLE 5.

CD28-B7 blockade of polysaccharide-induced CD4⁺ T-cell activation prevents abscess formation^a

T-cell stimulus	Fusion protein	No. of animals positive for abscesses/ total (%)	P
Medium		1/7 (14)
S. pneumoniae type 1 CP		8/8 (100)	0.0014b
S. pneumoniae type 1 CP	CTLA4Ig	0/8 (0)	0.0002c
S. pneumoniae type 1 CP	L6Ig	6/8 (75)	Not significantc

^aT cells and APCs were cocultured in vitro with polysaccharide (20 μg/ml) and fusion protein (50 μg/ml) for 4 days prior to harvest. T cells were enriched by nylon wool passage, depleted of CD8⁺ T cells by magnetic bead depletion, and administered to rats via the intraperitoneal route. SCC were administered to animals shortly thereafter. Animals challenged with T cells alone or SCC only did not form abscesses. 

^bCompared with medium-stimulated T cells. 

^cCompared with S. pneumoniae type 1 CP-stimulated T cells.