Antibody:	anti-SP-A
Detection system:	Biotinylated secondary antibody/[Strept]avidin coupled to horseradish peroxidase

Structure	Level	Pattern	Image	Note
TS21: lung epithelium	Present	Regionally restricted		Expression in epithelium of smaller airways; no expression in epithelium of larger airways.

Structure	Level	Pattern	Image	Note
TS22: lung epithelium	Present	Regionally restricted	1C	Expression in epithelium of smaller, more peripheral airways; expression tended to be continuous, strongest at luminal edge. Little or no expression in epithelium of larger proximal airways.

Structure	Level	Pattern	Image	Note
TS22: lung epithelium	Present	Regionally restricted		Gradient of expression from tall columnar epithelium of larger airways, with increasing expression in low cuboidal epithelium of smaller airways.

Structure	Level	Pattern	Image	Note
TS23: lung epithelium	Present	Regionally restricted		Expression confined to epithelium of small airways; maximal level of expression not as high as at E14.

Structure	Level	Pattern	Image	Note
TS24: lung epithelium	Present	Regionally restricted	2C	Reduced expression in epithelium of small airways in the center of the section relative to the periphery. No expression in the presumptive Clara cell population of large airway epithelium.

Structure	Level	Pattern	Image	Note
TS25: lung epithelium	Present	Regionally restricted		Increased numbers of non-expressing epithelial cells in small airways. No expression in large proximal airways.

Structure	Level	Pattern	Image	Note
TS26: lung epithelium	Present	Regionally restricted	4C	No expression in core of tall neuroendocrine cells in large NEB. Expression in cap of presumptive Clara cells covering luminal surface of NEB. Expression in Clara cell population in all large airway epithelium, extending into proximal small airways.
TS26: lung	Present	Regionally restricted	4C	Expression in of small dense clumps of noncellular material primarily in lumen of small distal airways.

Structure	Level	Pattern	Image	Note
TS26: lung epithelium	Present	Regionally restricted	4D	Expression in occasional cells, tentatively identified as differentiating Type II alveolar cells, in small airways near the periphery of the section.
TS26: lung	Present	Regionally restricted	4D	Weak expression in many scattered cells associated with small airways throughout the lung.