Volume 30, Number 10, October 2008 Splenic changes in visceral leishmaniasis Table 2 Perisplenits and red pulp changes in dogs from an endemic area of L. chagasi infection, with different patterns of response to the infection Total (%) 72 20 (28) 8 (11) 14 (19) 58 (81) 32 (44) 40 (55) 54 (75) 18 (25) 53 (74) 19 (26) 10 (14) 10 (14) 10 (14) 519 Parameters Number of animals Perisplenitis Red Pulp: Granuloma Plasma cells: Absent–few Average–frequent Macrophage: Absent–few Average–frequent Lymphoblasts: Absent-few Average-frequent Megakaryocyte: Absent-few Average-frequent Leishmania amastigotes: Positive histology: Sub-capsular Red pulp Parasite density: Sub-capsular Internal red pulp Animal groups Infected Potentially resistant to VL (%) 22 2 (10)a 0 (0) 5 (23) 17 (77) 13 (59) 9 (41) 19 (86) 3 (14) 14 (64) 8 (36) 0 (0) 0 (0)g 0 (0) 0 0 Potentially susceptible to VL (%) 25 18 (72)b 7 (28)c 1 (4) 24 (96) 15 (60) 10 (40) 17 (68) 8 (32) 19 (76) 6 (24) 10 (40)e 10 (40)e 10 (40)e 45 ± 40f,g 37 ± 44 Undeﬁned susceptibility status (%) 11 0 (0) 1 (9) 2 (18) 9 (82) 0 (0) 11 (100) 9 (82) 2 (18) 8 (72) 3 (27) 0 (0) 0 (0) 0 (0) 0 0 Noninfected (%) 14 0 (0)a 0 (0) 6 (43) d 8 (57) 4 (29) 10 (71) 9 (64) 5 (36) 12 (86) 2 (14) 0 (0) 0 (0) 0 (0) 0 0 aCapsular tissue was absent or poorly represented in one animal. b–fStatistically signiﬁcant differences (χ2-test with Yates’ correction): aP = 0.02; bdifferent from the other groups, P < 0.0001; cdifferent from the other groups, P = 0.0102; ddifferent from the other groups, P < 0·0366; edifferent from the other groups, P < 0.0001; fStatistically different from the parasite density in the internal red pulp (paired t-test, P = 0.0425). gExpressed as the mean of the relative (%) number of high power ﬁelds positive for amastigotes among 20–50 examined. the infected and potentially susceptible to VL group. In all of these animals, amastigotes were seen in both the sub- capsular area and the internal red pulp (Figure 1j–k). The parasite burden, measured as the proportion of positive ﬁelds among the examined high power ﬁelds, was higher in the subcapsular area (45 ± 40%) than the internal red pulp (37 + 44%; paired t-test, P = 0·0425). Although parasite distribution in the spleen was usually uneven, three animals with high parasite burden showed evidence of parasites in all of the examined ﬁelds (i.e. in the subcapsular area and in the internal red pulp). White pulp structural organization Distinction of the different regions inside the white pulp of the spleen was absent or poor in 17 (24%) out of 72 animals (Table 3 and Figure 1d–i). The frequency of animals with moderate or extensive structural disorganization of the white pulp areas was higher in the infected and potentially susceptible to VL group (14 out of 25 animals, 56%) than it was in the other groups (χ2-test, P < 0·0001). Lymphoid follicle frequency Lymphoid follicles were present in specimens from all of the animals (Table 3). The frequency of these follicles was rare or low in 36 (50%) out of the 72 animals. The frequency of animals with a low proportion of lymphoid follicles was higher in the infected and potentially susceptible to VL group (20 out of 25, 80%) than it was in the other groups (χ2-test, P = 0·001). Lymphoid follicle size Lymphoid follicles were tiny or small in 38 (53%) out of the 72 animals (Table 3). A higher proportion of animals with small or tiny lymphoid follicles was observed in the infected © 2008 The Authors Journal compilation © 2008 Blackwell Publishing Ltd, Parasite Immunology, 30, 515–524