Immune response, evasion

Phase variation (Salmonella) Hin/hix Site-specific Alternative expression of two flagellin genes allows evasion of host immune response. 

Oncospheres of many cestode species penetrate and develop into metacestodes within cysts (cysticerci, hydatid, multilocular) in the soft tissues of their rodent, ruminant or human hosts. Thus, species such as Echinococcus granulosus, E. multilocularis, Eaenia multiceps, T. ovis, E. saginata and E solium are of economic and medical importance. Such soft tissue invasion elicits a host immune response to resist the helminths. However, although some cysts may be destroyed as evidenced by involution or calcification, the host response is often too little - too late to eliminate the invaders. The susceptibility of the host to invasion is often due to successful evasive strategies... 

Many SCLC patients mount an antitumor immune response without signs of PNS [9, 167, 174]. Nevertheless, most SCLC patients do not have this immune response. Thus, the rarity of PNS cannot be attributed to infrequency of antigen expression. This discrepancy suggests that additional factors, perhaps related to tumor major histocompatibility complex (MHC) expression, contribute to the initiation of the PNS immune response. A study of Hu antigen and MHC class I expression in SCLC and neuroblastoma supports this theory. Seventeen of 20 tumors from Hu antibody positive patients expressed both proteins, but only 4 of 30 specimens from seronegative individuals expressed both proteins [171]. Altered expression and/or down-regulation of MHC molecules is a common immune-evasive strategy of tumor cells [175],... 

Antigenic variation (trypanosomes) Varies Nonreciprocai gene conversion Successive expression of different genes encoding the variabie surface giycoproteins (VSGs) aiiows evasion of host immune response. 

Evasion of host immunity. Implicit in the ability to invade is the ability to evade host responses that would block parasite migration or be directly lethal to the organism. Mechanisms by which parasite helminths evade the host immune response have been extensively analyzed and debated, and the reader is referred to the numerous reviews on this subject, particularly for the well-studied example of schistosomiasis (26). 

Schagen F H, Ossevoort M, Toes R E, et al. (2004). Immune responses against adenoviral vectors and their transgene products A review of strategies for evasion. Grit. Rev. Oncol. Hematol. 50 51-70. 

Scalsp In the case of MCMV we find quite a lot of genetic variation in some immune evasion genes. This results in differences in the immune response and how the virus escapes from different arms of the innate and adaptive immune response. 

Metastatic spread is an important aspect in tumor biology and usually determines the clinical behavior. The metastatic process is a long complicated multistep process which begins with tumor development and evasion of immune response and ends with the organization of metastatic tissue and the induction of tumor stroma and neovascularization (Table 1.1). 

Weber KS. Selective recruitment of Th2-type cells and evasion from a cytotoxic immune response mediated by viral macrophage inhibitory protein-II. Eur J Immunol 2001 31(8) 2458-66. 

The use of viral chemokine/receptor mimics and inhibitors identified in particular virus families such as herpesviruses, poxviruses and HIV indicates their importance in pathogensis of these viruses, either for evasion of the immune response as with poxviruses and herpesviruses or addtionally the use of recptors for viral entry as with HIV and poxviruses. Further studies will almost certainly identify a greater range of viruses producing such mimics. 

---