In order to understand the effect of prednisolone injection on the immune responses of albino rat against Paragonimus iloktsuenensis infection, the differential leucocyte counts, appearance of immunoblast (large pyroninophilic cell, LPC) in the spleen and lungs in various experimental groups were observed in relation with the growth, maturation and migration sites of this rodent lungfluke.

Rats of 3 experimental groups (A series), each group consisted of 5 rats, were infected with 20 metacercariae of P. iloktsuenensis, and they were kept for 3 days(Group I), 3 weeks(Group II), and 4 weeks (Group III) of infection period. The same number of experimental groups, each group of rats received 10 mg/kg dose of prednisolone injection every other day, were also kept and examined in comparison with the former groups.

Preparation of peripheral blood smear and collection of worms were completed immediately after the end of infection period, and they were stained with Giemsa or Semichon's acetocarmine. Paraffin sections of the spleen and the lung tissues were stained with hematoxylin-eosin and methyl green pyronin (MGP).

Those materials from A and B series of experimental groups were examined under the light microscope, and the results obtained were as follows:

1. On observing differential leucocyte counts of peripheral blood smear, lymphocyte counts were consistently higher than those of uninfected controls in A series of infected groups, while those of B series were consistently low.

On the other hand, neutrophil counts of A series showed lower counts than those of B series.

In general, fluctuation patterns of both A and B series of experimental groups were almost the same, although lymphocyte and neutrophil counts showed reciprocal relation. The eosinophil counts of both series were negligible, especially in the groups of B series.

2. The counts of LPC in the periarterial lymphatic sheath of the spleen were rapidly increased in the groups of A series, while those of B series were much less than those of A series, and the appearance of considerable LPC in the spleen was also delayed in B series. Furthermore, LPC of peribronchial lymphatic tissue in A series started to increase after the invasion of lungflukes into the lungs, while those of B series were much less due to the inhibited migration of lymphocytes into the lesions.

3. Number, size and maturity of collected worms showed no significant differences between the groups of A and B series, but migration speed of the lungflukes was somewhat accelerated in B series than in A series.

In this connection, it was considered that the immune responses of albino rats did not contribute for the complete protection against P. iloktsuenensis, but inhibited the migration of this lungfluke to some extent.