Fig. 3

Heterologous immunization with late-arresting attenuated sporozoites leads to higher secondary CD8⁺ T cell responses to the L3 antigen in BALB/cj mice. a L3-specific responses in BALB/cj mice immunized homologously with P. yoelii RAS (Py/Py) or heterologously with P. berghei RAS followed by P. yoelii RAS (Pb/Py). Heterologous immunization showed a small non-significant increase in L3-specific responses. b L3-specific responses in BALB/cj mice immunized with P. yoelii fabb/f ^−/− GAP (PyGAP) or homologously with P. yoelii RAS followed by P. yoelii GAP (PyRAS/PyGAP) or heterologously with P. berghei RAS followed by P. yoelii GAP (PbRAS/PyGAP). Homologous immunization showed the typical contraction of the L3-specific response, whereas heterologous exposure resulted in a significant increase relative to homologous levels. In some cases, mice mounted extremely strong L3 responses following secondary heterologous exposure that were never seen following primary exposure. **p < 0.01, ***p < 0.001, Student’s t-test. All injections were 1 × 10⁴ sporozoites by intravenous route