Testicle Infection in Guinea Pigs Sensitized with Killed Tubercle Bacilli
Authors: Stewart Fred W. 
Published: December 2022

Summary and Conclusions
A positive intradermal reaction to old tuberculin diluted with 19 parts physiological saline may be obtained in guinea pigs previously injected with certain amounts of killed tubercle bacilli.
Subsequent testicular infection with the B-1 strain of tubercle bacillus causes in a sensitized animal within forty-eight hours slight edema, a heavy deposit of fibrin, a marked infiltration by polymorphonuclear leucocytes, many eosinophiles, mitoses in endothelial leucocytes and in fixed endothelial cells. The germinal epithelium becomes vacuolated, many immature cells slough off into the lumina of tubules, forming often multinucleated epithelial giant cells. Tubules of the epididymis become filled with immature sex cells, polymorphonuclear leucocytes and phagocytic endothelial leucocytes.
The control animal exhibits a slight infiltration by polymorphonuclears, eosinophiles, lymphocytes and endothelial leucocytes. A trace of fibrin, no edema, and a normal epithelium characterizes early stages. Mitoses are seen in endothelial leucocytes and fixed endothelium; in other words, the sensitized shows a much greater exudative reaction and a more marked, though not earlier, proliferative (endothelial) reaction.
Necrosis of tubules and possible thromboses cannot be excluded as important factors in the initiation of a marked polymorphonuclear reaction in the sensitized.
Hemorrhage may occur in the sensitized testis.
Abscesses occur both in sensitized and control animals. They appear earlier and are larger and more numerous in the sensitized testis.
Phagocytosis of polymorphonuclear leucocytes by endothelials occurs in both and varies with the number of polymorphonuclears present in the exudate.
An eosinophile reaction occurs in both control and sensitized, is inconstant, and tends to disappear as the tuberculosis progresses. It cannot be shown to be associated with sensitization.
As the disease progresses the architecture of the testis becomes disorganized—much earlier in the sensitized than in the control. Tubules are gradually lost, their cells becoming indistinguishable in masses of polymorphonuclears, endothelial leucocytes, giant cells and fibroblasts. Remnants of tubules may persist as bright eosin-staining debris in the midst of such masses. Much of the epithelium undergoes phagocytosis.
Proliferation of fibroblasts occurs earlier and to greater extent in the sensitized testis, but occurs in the control before a positive skin reaction is obtained.
Every histological characteristic of the sensitized testis, though to lesser degree, may be encountered in the control testis before the intradermal test has become positive and in consequence no one histological feature may be said to characterize the reaction to reinfection in the testis of an animal generally sensitized to tuberculin. The differences are only those of degree, both in time and in amount of exudative and proliferative reactions.
The presence of early necrosis in the sensitized testis makes it impossible to decide whether the acuteness of reaction is a more rapid formation of “protective” tissue or a response to necrosis. The two may not be mutually exclusive.
After the sixth day little or no difference is seen between control and sensitized. Eventually caseation occurs in both.
In this series it was not shown that sensitization has any protective value; in fact the controls showed rather less disease.
The above conclusions apply to a given organ, given sensitization, and to certain infecting quantity of the B-1 strain of tubercle bacillus. They must be interpreted only as such.