212 
PULMONARY MODELS 
Figure 3. — Cat alveolar capillaries after onset of perfusion in a dog. There is extreme capillary congestion with 
packed red cell masses appearing as bead-like projections. Occasional polymorphonuclear leucocytes are seen, 
but they are never seen in groups or increased numbers. This biopsy was taken two minutes after the dog's 
circulation was established to the cat's lung. 
very few if any blood cells (Fig. 5) . Leukocyte 
and platelet aggregates were not found in the 
erythrocyte plugs. 
In addition to observations in the trans- 
planted lung, we have made observations in cat- 
to-dog renal xenografts. Here the same type of 
early intravascular erythrocyte aggregation 
was seen occurring in cortical capillaries located 
between distal convoluted tubules. 
DISCUSSION 
Hyperacute rejection can occur with widely 
divergent xenografts and when allografts are 
transplanted into a previously sensitized reci- 
pient who has circulating antibodies to the 
graft.3'^1 This process leads to rapid cessation 
of blood flow and destruction of the trans- 
planted organ. To better understand this phe- 
nomenon, it is necessary to delineate its prog- 
ress and causes. It is also important to reconcile 
some of the discrepant histologic findings re- 
ported in the literature. The present study was, 
there fore, undertaken to provide a morphologic 
examination of the developing pathology in 
vivo. 
Although a large literature exists on hyper- 
acute rejection in kidneys, we are unaware of 
any description of this process in the lung.^'^"'" 
Our study shows that pulmonary hyperacute re- 
jection, like hyperacute renal graft rejection, is 
charcterized by a rapid cessation of graft blood 
flow. In contrast to hyperacute renal rejection, 
however, it appears that hyperacute rejection 
in the lung is, at first, a focal phenomenon. This 
