W. p. SWITZER 
1017 
Studies are now being undertaken to deter- 
mine if the stimulation of antibodies by the 
administration of bacterins of adequate potency 
will produce rapid and reliable enough clearance 
of the chronic carrier state to break the genera- 
tion to generation transmission of this disease. 
If this proves to be the case then such bacterins 
will be of great practical value in the control 
of this disease even though they are not ca- 
pable of preventing the initial infection. Such 
bacterins may work through increased efficiency 
of phagocytic removal of the surface infection. 
Consideration of the mechanism of the im- 
mediate resistance of the nasal cavity of swine 
recovered from virulent or low virulence B. 
bronchiseptica infection, either as a result of 
natural recovery or sulfonamide medication, is 
more complex. Several facts appear to afford a 
partial explanation. It has been clearly demon- 
strated that this bacterium attaches to swine 
nasal epithelial cells.^ This is probably the first 
prerequisite for the successful colonization of a 
ciliated epithelium. If some provision for an- 
choring of the bacteria against mechanical re- 
moval is not available, then the infectious par- 
ticle would simply be transported on the 
muco-ciliary escalator to where it could be swal- 
lowed. Epithelial attachment is probably a re- 
quirement for any bacteria or mycoplasma to 
colonize functional ciliated epithelium. It has 
also been demonstrated that one of the early 
tissue damages in the area of a micro-colony of 
B. bronchiseptica on ciliated epithelium is the 
disruption of the cilia.^ This affords a micro- 
colony of this organism an additional defense 
against removal. 
Bordetella bronchiseptica also produces a 
hemagglutinin. There is some preliminary evi- 
dence that the epithelial and the red blood cell 
attaching substance are somewhat similar, if 
not the same. There is preliminary evidence 
that nasal secretions collected from resistant 
swine have some activity in inhibiting bacterial 
hemagglutination. In order to complete our un- 
derstanding of this basis for resistance it still 
must be established that the immediate resist- 
ance of the recovered swine nasal cavity is due 
to a blockage of the epithelial receptor sites on 
either the bacteria or the epithelial cells by some 
component in the nasal secretion. Some avail- 
able information points in this direction. Of 
importance is the development of a particular 
antigen settling test (PAST)" that is up to 80 
times more sensitive in measuring serum and 
secretion factors stimulated by recovery from 
this infection. The basis of this test is an altered 
settling pattern of a standardized bacterial sus- 
pension. At the more concentrated levels of se- 
rum or nasal secretions this is essentially a 
microagglutination test. At the higher dilution 
of test material, the agglutination aspect is left 
behind and the test is dependent on substances 
coating the organisms in such a manner that the 
settling and surface adhesion pattern of the 
cells is altered. We have demonstrated PAST 
titers in nasal secretions of resistant, recovered 
pigs even though no agglutinating antibody 
titers can be detected. The sera of bacterin in- 
jected and chronically infected swine contain 
both agglutinating and PAST substances.'^ The 
latter are almost always present at higher 
titers. 
The possible blockage of bacterial attachment 
sites by factors present in the nasal secretion 
with subsequent disposal of the bacteria by re- 
moval on the muco-ciliary escalator, projects 
the muco-ciliary surface into a possible role as 
the first line of immunologic defense against 
bacterial and mycoplasmal respiratory infec- 
tions. 
SUMMARY 
Most attention has been given to the produc- 
tion of circulating antibodies and the passage 
of certain portions of these antibodies into the 
respiratory secretions. Secretory antibodies 
are certainly important defenses but preoccupa- 
tion with them may cause primary "first line" 
resistance factors to be overlooked. 
REFERENCES 
1. Duncan, J. R., Ross, R. F., Switzer, W. P., and 
Ramsey, F. K. Pathology of Experimental Borde- 
tella bronchiseptica Infection in Swine: Atrophic 
Rhinitis. Am. J. Vet. Res. 27:457-466, 1966b. 
2. Duncan, J. R., and Ramsey, F. K. The Structural 
Changes in the Porcine Nasal Ciliated Epithelial 
Cell Produced by Bordetella bronchi septica Rhi- 
nitis. Am. J. Path. 47:601-612, 1965. 
