Abstract
Tissue reactions against Coccidioides immitis infection were investigated.
Congenitally athymic nude mice (nu/nu), their heterozygous littermates (nu/+) and ddY mice were used as experimental animals. Each mouse was inoculated intravenously with 3.3×105 or 530 of arthroconidia and was sacrificed at determined intervals for histological examination.
The virulence of C. immitis used in this experiment was as follows: When 3.3×105 arthroconidia were inoculated intravenously, all of 6 nu/nu or 6 nu/+ mice died 5 or 6 days after inoculation, respectively. When 530 arthroconidia were inoculated, all of 6 nu/nu or 6 nu/+ mice died 14 or 13 days after inoculation, respectively.
The parasitic cycle of the fungus in the mouse organs was completed within 5 days.
As the C. immitis had predilection for the liver, spleen and lung, we focussed on the liver to investigate the tissue reactions.
Without distinction among mouse strains, cell reactions to the arthroconidia were very weak. A few polymorphonuclear leucocytes (PMN), monocytes or a mixture of the two accumulated at the arthroconidia. This pattern of cell infiltration continued until the completion of spherules; it took about 4 days.
When part of the cell wall of a spherule was broken down and numerous endospores were release into the tissue, PMN accumulated immediately and remarkably at the endospores and formed relatively large pyogenic lesions 4 days after inoculation, in which most of the released endospores were destroyed by the PMN. On the 7th day, lesions changed to granulomatous ones, and surviving endospores began to be destroyed in the granulomatous lesions.
In the nu/nu mice, granulomatous lesions were formed 7 days after inoculation. However, different from the granulomatous lesions formed in the nu. + and ddY mice, endospores released from spherules were not destroyed in the granulomatous lesions and continued to develop into mature spherules.
