C.C. Santana et al. Parasite Immunology Table 3 White pulp changes in dogs from an endemic area of L. chagasi infection, with different patterns of response to the infection a–eStatistically different from the other groups (χ2-test with Yates’ correction): aP < 0·0001; bP = 0·0010; cP<0·0036; dP = 0·044; eP = 0·0015; fP = 0·0162; gP = 0·0025. Parameters Number of animals White Pulp Structural disorganization: Absent – Slight Moderate – Extensive Lymphoid follicle: Frequency Rare – Low Average – High Size Tiny – Small Average – Large Germinal centre: Size Absent – Small Average – Large Marginal zone: Size: Absent – Small Average – Large Animal groups Infected Potentially resistant to VL (%) 22 21 (95) 1 (5) 6 (27) 16 (73) 6 (27) 16 (73)d 6 (27) 16 (73)f 5 (23) 17 (77) Potentially susceptible to VL (%) 25 11 (44) 14 (56)a 20 (80)b 5 (20) 20 (80)c 5 (20) 21 (84)e 4 (16) 15 (60) g 10 (40) and potentially susceptible to VL group (20 out of 25 animals, 80%) than other groups (χ2-test, P = 0·0036). In contrast, the frequency of animals with large follicles in the infected and potentially resistant to VL group (16 out of 22 animals, 73%) was higher that in the other groups (χ2-test, P = 0·044). Germinal centre size Germinal centres were absent or small in 39 (54%) out of the 72 animals (Table 3). The frequency of animals with lymphoid follicles containing small, tiny, or the absence of germinal centres was higher in the infected and potentially susceptible to VL group (21 out of 25 animals, 84%) than other animal groups (χ2-test, P = 0·0015). Conversely, the frequency of animals with average or large germinal centres was higher in the infected and potentially resistant to VL group (16 out of 22 animals, 73%) than the other groups (χ2-test, P = 0·0162). Marginal zone size The marginal zone was absent, tiny, or small in 25 (35%) out of the 72 animals (Table 3). The proportion of animals with 520 Undeﬁned susceptibility status (%) 11 10 (91) 1 (9) 2 (18) 9 (82) 4 (36) 7 (64) 5 (45) 6 (55) 2 (18) 9 (82) Noninfected (%) 14 13 (93) 1 (7) 8 (57) 6 (43) 8 (57) 6 (43) 7 (50) 7 (40) 3 (21) 10 (79) Total (%) 72 55 (76) 17 (24) 36 (50) 36 (50) 38 (53) 34 (47) 39 (54) 33 (46) 25 (35) 47 (65) marginal zones that were small, tiny, or absent was higher in the infected and potentially susceptible to VL (15 out of 25 animals, 60%) than the other animal groups (χ2-test, P = 0·0025). The marginal zone size was moderately correlated with lymphoid follicle size (Spearman r = 0·5247, P < 0·0001, Figure 2a) and germinal centre size (Spearman r = 0·5354, P < 0·0001, Figure 2b). Associations between morphological changes in the spleen and emaciation Evidence of weight loss was present in 27 (39%) out of the 69 animals from which data were recorded. Weight loss was more frequent in the infected and potentially susceptible to VL group than other groups (χ2-test, P = 0·02). Being underweight was associated with the following alterations in the splenic tissue. First, it was associated with disorganization of the white pulp structure. Among the 27 animals with emaciation, 19 (70%) had some degree of white pulp disor- ganization; only 18 (43%) out of 42 animals with normal nutritional status had loss of white pulp architecture deﬁnition (χ2-test, P = 0·0467). This association between © 2008 The Authors Journal compilation © 2008 Blackwell Publishing Ltd, Parasite Immunology, 30, 515–524